In this Oct. 30, 2018 photo, Democratic Sen. Joe Donnelly, left, shakes hands with Republican former state Rep. Mike Braun following a U.S. Senate Debate in Indianapolis. Republicans have a huge advantage as they seek to hold or expand their 51-49 Senate majority, with the battle for control running mostly through states that President Donald Trump won in 2016. (AP Photo/Darron Cummings, Pool)

In this Oct. 30, 2018 photo, Democratic Sen. Joe Donnelly, left, shakes hands with Republican former state Rep. Mike Braun following a U.S. Senate Debate in Indianapolis. Republicans have a huge advantage as they seek to hold or expand their 51-49 Senate majority, with the battle for control running mostly through states that President Donald Trump won in 2016. (AP Photo/Darron Cummings, Pool)

WASHINGTON (AP) — Republicans have a huge advantage as they seek to hold or expand their 51-49 Senate majority, with the battle for control running mostly through states that President Donald Trump won in 2016.

Out of the 35 Senate contests taking place Tuesday, 10 involve Democratic incumbents seeking re-election in states that Trump won, often handily. He’s spending much of the final week before the election traveling to those states in the hope that it will nudge his supporters to the polls.

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Meanwhile, Democratic hopes of taking the Senate hinge on nearly all of their incumbents winning — a difficult task — and on flipping seats in a few states that lean Republican, most notably Arizona, Tennessee and Texas.

Trump is pushing back on the idea that the election is a referendum on him, though he’s also boasted of helping Republicans in key Senate races with his frequent campaign rallies.

Key races to watch for those keeping score, listed in order of poll-closing times:

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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

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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

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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. Nelson has stressed that he favors a ban on military-style assault weapons and implementing a comprehensive system of background checks. Scott signed legislation in Florida that requires anyone wanting to buy a gun to be 21 years old, but the bill didn’t include a ban on assault weapons.

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

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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 recently 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

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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.”

Democratic groups have spent millions in the state to boost Menendez in his race against Republican Bob Hugin, a former pharmaceutical executive who has tapped his own wallet for $24 million to finance a TV-ad-heavy campaign.

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

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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

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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 that is 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.

McSally accused Sinema of “treason” for comments about the Afghanistan war in 2002, while Democrats have been hammering McSally for her vote to repeal President Barack Obama’s health care law.

Polls close at 9 p.m. EST

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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 on trade must be given time to work.

Heitkamp’s campaign stumbled when it identified victims of domestic violence, sexual abuse and rape in an ad. Heitkamp apologized after she learned that several of the women named in the newspaper ad either hadn’t authorized being named or are not survivors of abuse.

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

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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

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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

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For AP’s complete coverage of the U.S. midterm elections: http://apne.ws/APPolitics