It's Election Day and Americans are already lining up at polling places to cast their votes.
Voters will elect a new House of Representatives – all 435 seats are in play – and will vote in 35 U.S. Senate elections. In 36 states, governors will be elected.
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What is at stake in this election, when will we know the results, who will win? Here's a look at how the day will shape up and the races you should watch if you want to handicap the races this evening.
What is at stake?
All 435 seats in the U.S. House of Representatives are up for election on Tuesday, and a little more than one-third of the U.S. Senate seats (35) are on ballots across the country.
Currently, Republicans have the majority in both the House and the Senate.
In the House, Republicans hold a 235-to-193 majority (seven seats are vacant), and in the Senate, the GOP has a 51-to-49 edge.
Which races should I watch Tuesday?
Will you be able to see a nationwide trend by the outcome of a few races? Some political pundits think there are bellwether races that would signal a good night for Democrats or Republicans, depending on how they break.
Here, from The Associated Press, are a few races that may give you a hint as to how the night will go.
In the House:
Kentucky – District 6
The ruby-red state, known for the Kentucky Derby and sweet bourbon, is hosting one of the most competitive and expensive races in the country. The Lexington-area battle pits third-term Republican Rep. Andy Barr against Democrat Amy McGrath, a retired Marine fighter pilot. Trump won the 6th District by more than 15 percentage points in 2016. But with the help of carefully shaped campaign ads that went viral, McGrath holds the edge on campaign fundraising.
Polls in the district close at 6 p.m. EST
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Georgia – District 6
Red-hot Georgia is home to a House race that turns on issues of race and gun laws. Republican Rep. Karen Handel narrowly won her seat in a special election last year that set a record for spending. Now her Democratic challenger is Lucy McBath. The district north of Atlanta leans Republican, but Trump won it by only 1 percentage point.
Polls close at 7 p.m. EST.
Virginia – District 7
Rep. Dave Brat won his seat after upsetting House Majority Leader Eric Cantor in the 2014 Republican primary. Now, it's Brat's turn to fight for re-election to the Richmond-area district against Democrat Abigail Spanberger, a former CIA officer who is one of a record number of women running for Congress this year.
Polls close at 7 p.m. EST
North Carolina – District 9
North Carolina's 9th District became a key election bellwether when the Rev. Mark Harris narrowly ousted three-term Rep. Robert Pittenger in the GOP primary, giving Democrats a wider opening in solidly red territory. Democrats answered with Dan McCready, an Iraq War veteran, solar energy company founder and Harvard Business School graduate. Trump won the district by 12 points and a Democrat hasn't been elected to represent it since John F. Kennedy was president.
Polls close at 7:30 p.m. EST
Ohio – District 12
It's a rematch in central Ohio's 12th District between Republican Troy Balderson and Democrat Danny O'Connor. Balderson won short-term control of the seat in August during a special election after Republican Pat Tiberi retired. Republicans in the district appear divided over the president, making the seat vulnerable to a Democrat who, like O'Connor, has supported some Republican ideas. He's engaged to a Republican who calls herself a "Dannycrat."
Polls close at 7:30 p.m. EST
Florida – District 27
National Republicans and Democrats are pouring major resources into the Miami-area 27th District seat, held since 1989 by retiring Republican Rep. Ileana Ros-Lehtinen. The Democratic nominee, former Health and Human Services Secretary Donna Shalala, has ramped up her Spanish-language advertising and Hillary Clinton campaigned for her. But she's facing a stiff challenge from her Republican opponent, Maria Elvira Salazar, a Cuban-American and former broadcast journalist who, unlike Shalala, speaks Spanish. Though Trump won Florida in 2016, Clinton won this congressional district by nearly 20 points.
Polls close at 8 p.m. EST
New Jersey – District 3
Along with California and Pennsylvania, suburb-filled New Jersey is a key battleground for House control. Keep a close eye on the 3rd District south of Trenton, which twice voted for President Barack Obama but went for Trump by about 6 percentage points. Fighting for re-election is Republican Rep. Tom MacArthur. His Democratic opponent is political newcomer Andy Kim, a National Security Council staffer under Obama who has worked in Afghanistan.
Polls close 8 p.m. EST
Pennsylvania – Districts
Democrats have particular reason to believe they can flip as many as six seats in the Keystone state.
One key race is playing out in the Philadelphia suburbs. Freshman Republican Rep. Brian Fitzpatrick, a former FBI agent, has a centrist voting record and has explicitly tried to put distance between himself and Trump. He's facing Scott Wallace, a longtime Democratic Party donor who was co-chairman of the Wallace Global Fund, a Washington, D.C.-based organization that supports liberal social movements. He's heavily funding his campaign and outspent Fitzpatrick nearly 5-to-1 in the July-September quarter.
Polls close at 8 p.m. EST.
Kansas – District 2
Trump and House Democratic Leader Nancy Pelosi loom large over a race in Northeastern Kansas. That's where Democrat Paul Davis, the former state House minority leader, and Republican Steve Watkins, an Army veteran and engineer, are battling for the seat vacated by retiring Democratic Rep. Lynn Jenkins.
Polls close 9 p.m. EST
Minnesota – District 3
Four House seats could flip from one party to the other in this traditionally Democratic stronghold.
For evidence of Democratic gains, look to the state's booming suburbs. Clinton won Minnesota's 3rd District west of Minneapolis by 9 percentage points. GOP Rep. Erik Paulsen is under heavy pressure from Democrat Dean Phillips there. Paulsen avoided Trump's recent rally in Rochester and his rally this summer in Duluth, and he has said he wrote in Marco Rubio's name in the 2016 election. Still, Trump endorsed Paulsen last month.
Polls close 9 p.m. EST
New Mexico – District 2
The open 2nd District seat left open by Republican Rep. Steve Pearce, who is running for governor, offers a look at how the parties fare along the border with Mexico, where registered Democrats outnumber Republicans. The race between Democrat Xochitl Torres Small and GOP opponent Yvette Herrell has focused on hot-button issues such as immigration and guns. Torres Small has raised more than five times the campaign cash drawn by Herrell.
Polls close 9 p.m. EST.
New York – Districts 19, 22
This deep-blue state offers a look at how race and Trump's clout are playing out in the president's home state.
North of New York City in the 19th District, an ad released last month by the Republican National Congressional Committee showed clips of Democrat Antonio Delgado performing songs from his 2006 rap album under his stage name, A.D. The Voice. Delgado, a Rhodes scholar and Harvard Law School graduate, said his opponent, Rep. John Faso, was using racial attacks to alienate him, a black first-time candidate in a district that is more than 90 percent white.
And in the Buffalo area's 22nd District, first-term Rep. Claudia Tenney, an early Trump supporter, is drawing comparisons to the president by brashly suggesting some people who commit mass murders are Democrats and promoting a petition to lock up Clinton. But in a close race against Democrat Anthony Brindisi, she's shifted to a softer tone of bipartisanship. Brindisi, a state assemblyman, argues that Tenney's hyper-partisan approach undermines her claim of working across the aisle. Trump beat Clinton by nearly 16 percentage points here.
Polls close 9 p.m. EST.
Iowa – District 4
One Iowa race offers a test of whether a Trump-style advocate for immigration limits can win.
Republican Rep. Steve King is keeping a low profile in his bid for a ninth House term, his success suddenly in question after he was engulfed in controversy for his support of white nationalists. But Democrats, already hoping to flip two other seats among Iowa's four-person delegation, have a tough road to success in the 4th District that voted for Trump by 27 percentage points.
In an unusual move, the GOP's campaign chief condemned King the week before the election, but it's unclear whether the criticism will boost his Democratic opponent, J.D. Scholten.
Polls close 10 p.m. EST.
California – Districts 10, 48
Democrats have targeted a string of Republican-held districts in California that carried Clinton in the 2016 presidential election.
One such battleground in the nation's fruit-and-nut basket, the Central Valley, is where Republican Jeff Denham is trying to keep Democrat Josh Harder from taking his job. The fallout from Supreme Court Justice Brett Kavanaugh's confirmation hearings and fights over health care and immigration have produced a tossup race where Democrats count a slender registration edge. Denham, a centrist who voted to repeal the Affordable Care Act, won re-election by 3 percentage points in 2016, while Clinton won the district with about 49 percent of the vote.
Polls close at 11 p.m. EST.
Washington State – District 3
Southwest Washington's 3rd District offers a test of whether the tea party-driven GOP House takeover in 2010 survives. Republican Rep. Jaime Herrera Beutler, first elected that year and twice re-elected with more than 60 percent of the vote, has been out-raised in campaign funding by Democrat Carolyn Long. Herrera Beutler has broken with her party on such issues as health care. But Long has emphasized her credentials as an outsider. The district stretching east along the Oregon border voted for Trump by 7 percentage points.
Polls close at 11 p.m. EST.
In the Senate
Indiana
Democratic Sen. Joe Donnelly is trying to fend off Republican businessman Mike Braun in a state that Trump won by 19 percentage points. Donnelly is Indiana's lone Democrat elected statewide and has sought to align himself with Trump on the hot-button issue of expanding the border wall with Mexico. He has portrayed himself as a moderate who works with both parties to pass legislation. "I go against my party all the time," he said recently.
Braun has sought to question Donnelly's independence and describes him as a career politician. He notes that Donnelly supported Hillary Clinton's bid for the presidency and sided with the vast majority of Democratic senators in voting against the confirmation of Supreme Court Justice Brett Kavanaugh.
Polls close at 7 p.m. EST
West Virginia
Democratic Sen. Joe Manchin is a former governor in search of a second full Senate term representing a state that supported Trump by a whopping 42 percentage points in 2016. His opponent is Patrick Morrisey, a two-term state attorney general and staunch Trump supporter.
Manchin has made maintaining health care protections for pre-existing conditions a major focus of his campaign and has hit Morrisey for joining a lawsuit challenging the constitutionality of the Affordable Care Act. On major issues, Manchin did join Democrats in voting against the tax cuts, but he broke with his caucus and supported both of Trump's Supreme Court nominees, Neil Gorsuch and Brett Kavanaugh.
Morrisey calls Manchin a liberal who only acts bipartisan around Election Day.
Polls close at 7:30 p.m. EST
Florida
Democratic Sen. Bill Nelson is seeking a fourth term in the race against Republican Gov. Rick Scott. Scott has spent millions of dollars out of his own personal fortune to help fund his campaign. He has said that he would work to cut taxes and regulation if sent to Washington.
The two have clashed sharply on gun violence, a big issue in Florida following the February shootings at Marjory Stoneman Douglas High School.
The two have also differed on health care, with Nelson calling for strengthening the Affordable Care Act, but Scott calling the law deeply flawed and costly.
Polls close at 8 p.m. EST
Missouri
Democratic Sen. Claire McCaskill is running for a third term against state Attorney General Josh Hawley. Trump won Missouri by nearly 19 percentage points, and the state has shifted from a battleground to strongly Republican in recent elections.
McCaskill is touting herself as a moderate: "Claire's not one of those crazy Democrats. She works right in the middle and finds compromise," says one of her recent radio ads.
Hawley says of McCaskill that on any issue important to Missourians, "she's with her party down the line."
Trump has traveled several times to Missouri to campaign for Hawley, repeatedly describing the state's 38-year-old attorney general as a "star."
Polls close at 8 p.m. EST
New Jersey
Democratic Sen. Robert Menendez is facing a tough re-election fight, and it has nothing to do with Trump. Rather, allegations of corruption have alienated some New Jersey voters. His bribery trial ended last year with a hung jury. Prosecutors decided not to retry the case, but the Senate Ethics Committee followed up with a report that said his actions advancing the personal and business interests of a top donor "reflected discredit upon the Senate."
Democrats have more than 900,000 additional registered voters than Republicans in New Jersey, and Trump's low ratings in the Garden State could give Menendez a boost.
Polls close at 8 p.m. EST
Tennessee
Republican Rep. Marsha Blackburn is running against former two-term Democratic Gov. Phil Bredesen in a state Trump won by 26 percentage points.
Blackburn would be the state's first female senator if elected. She has served eight terms in the House and is viewed as one of the more conservative members of that chamber.
Bredesen is trying to brandish his credentials as a centrist. He has said he will support or oppose Trump based on his specific ideas and how they affect Tennessee.
The two are running to replace retiring Sen. Bob Corker, a Republican who has frequently clashed with Trump.
Polls close at 8 p.m. EST
Arizona
Democrats have high hopes for flipping this seat in Arizona, where Democratic Rep. Kyrsten Sinema is running against Republican Rep. Martha McSally.
They are running for the seat left open when Sen. Jeff Flake, a sharp critic of Trump, opted to retire, acknowledging that he could not win a GOP primary in the current political climate.
McSally is a former Air Force fighter pilot who represents a moderate district based in Tucson. Sinema represents a district based in the Phoenix suburb of Tempe and is a former Green Party activist who transformed herself into a centrist Democrat.
Polls close at 9 p.m. EST
North Dakota
Democratic Sen. Heidi Heitkamp is trying to fend off a strong challenge from Republican Rep. Kevin Cramer in a state Trump won by 36 percentage points.
Heitkamp has sought to draw differences with Cramer on health care and trade. She says she is working to improve the Affordable Care Act while he's been working to eliminate it. Cramer has argued that President Donald Trump's approach to trade must be given time to work.
Polls close at 9 p.m. EST
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Texas
Republican Sen. Ted Cruz is seeking a second term against Democratic Rep. Beto O'Rourke, a rising star in the Democratic Party who has shattered Senate campaign fundraising records despite shunning donations from outside political groups.
O'Rourke is trying to become Texas' first Democrat to win statewide office since 1994 but faces long odds given the advantage that GOP candidates have in statewide elections.
Cruz has made nice with Trump despite the ugly words they exchanged during the presidential campaign in 2016. Trump held a campaign rally for Cruz in Houston, calling the candidate "Beautiful Ted."
Polls close at 9 p.m. EST
Montana
Democratic Sen. Jon Tester is seeking a third term against Republican Matt Rosendale, Montana's auditor.
Trump has invested heavily in the race with four trips to a state he won by more than 20 percentage points. Rosendale has returned the admiration, describing himself as a Trump conservative.
Trump has blamed Tester for derailing the nomination of White House doctor Ronny Jackson to head the Veterans Affairs Department.
Facing all the GOP's firepower, Tester has stuck with the populist approach that worked for him in his 2006 and 2012 elections, highlighting his life as a grain farmer and even the three fingers he lost as a child in a meat grinder.
Polls close at 10 p.m. EST
Nevada
Republican Sen. Dean Heller is seeking a second full term against Democratic Rep. Jacky Rosen in the one true battleground state that features a Republican incumbent.
Heller and Trump have embraced each other after a rocky start, with both highlighting their desire to get more of the president's judicial nominees confirmed, a top priority for many social conservatives.
Heller is the only Republican running for re-election in a state Hillary Clinton carried in 2016.
Rosen is a first-term congresswoman who could benefit from a wave of Democratic and female activism fueled by opposition to Trump.
Polls close at 10 p.m. EST
What about the early vote?
A very large number of Americans have already voted. According to the AP, 36.4 million votes have been cast in advance of Election Day. Thirty states report that their early vote totals exceed the number of votes cast in advance of the 2014 midterm election.
University of Florida professor Michael McDonald, who studies voting patterns, told the AP that about 45 percent of eligible voters could cast ballots this year, well above the usual 40 percent turnout level.
What's the weather like?
If the forecast holds, every state east of the Mississippi River will likely see rain today. In the West, skies should be clear, and temperatures cool.
Tornadoes have been reported in Louisiana and Mississippi, and severe weather has been seen in Tennessee with power outages reported.
Voter turnout could be affected. According to Mike Bender of the University of North Florida, voters affected by weather are those who vote only occasionally, and they tend to be more liberal. If that is the case, the weather may tend to help the Republicans today.
When will we know the results?
That is always the question on Election Day. Many of the contested House seats are in the Eastern part of the country where polls close by around 8 p.m. EST. For a list of the times when polls close, see this story: Election Day 2018: What time do the polls close?
Who will win tonight?
We won't know until Wednesday is the answer most pollsters will give you. Nate Silver of fivethirtyeight.com predicts that Democrats are more likely to win the House and Republicans are lined up to keep the Senate.
But, he warns, that is just what research based on polls tells you. Click here for a good explanation as to why one party or the other is not certain to win an election, but may be more likely to.
What does it mean for Trump if the Democrats take the House?
What will happen to Trump's presidency if the Democrats win the House? It will make his next two years in office more difficult.
The House is the place where bills that raise revenue must originate. It is also the place where investigations can spring anew over just about anything Democrats would want to investigate.
Trump's tax returns would likely be subpoenaed.
How can I follow along?
We will begin continual live updates at 4 p.m. ET and continue all night and throughout Wednesday with up-to-the-minute results. Join us here then.
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