By Richard Cowan and Susan Cornwell
WASHINGTON, Nov 8 (Reuters) - As voters head to the polls in Tuesday's U.S. election, hopes have dampened among Democrats that they will make major gains in the U.S. Congress, even if their nominee, Hillary Clinton, wins the presidency.
Enough wind may have come out of Clinton's sails to slow the Democrats' Senate and House of Representatives headway because of the FBI's startling announcement last month that reignited the controversy about her email practices, congressional aides and analysts said.
If that is the case, they said, Republicans will likely defend their House majority and may be able to retain some Senate seats long seen as vulnerable to Democratic capture.
Americans will be voting to choose Clinton or Republican Donald Trump for president, and to fill 34 of the 100 Senate seats and all 435 House seats. Both the House and Senate are now controlled by the Republicans.
Polling website RealClearPolitics was reporting no clear trend in polling in key House and Senate races on Monday, with Republicans up in some swing states and Democrats in others.
An analysis of Senate races issued on Monday by political scientist Larry Sabato's "Crystal Ball" project at the University of Virginia projected the election would end with Democrats and Republicans each holding 50 seats.
Continued Republican dominance in Congress could stymie any legislative agenda put forth by Clinton. A Trump victory, along with a Republican Congress, could mean a swift end for Democratic President Barack Obama's Obamacare health reforms.
A senior Democratic aide said the Clinton emails controversy, which erupted again after FBI Director James Comey said on Oct. 28 his agency would examine newly discovered emails that might pertain to her use of a private server while secretary of state, could reduce by at least 10 the number of House seats Democrats may capture from Republicans.
Comey told Congress on Sunday that after the latest review, he was standing by his July decision that no criminal charges were warranted against Clinton.
But coming only two days before the election, Comey's latest announcement may have been too late for Democrats hoping to regain control of the House for the first time since 2010 and the Senate for the first time since 2014.
"It's terribly damaging to us," the Democratic aide said, adding Democrats could end up gaining only 12 to 16 House seats on Tuesday, instead of the 30 needed to win control of the chamber.
To win control of the Senate, Democrats would have to score a net gain of five seats. Republicans currently hold 54 Senate seats to 44 Democratic seats and two independents who align themselves with Democrats.
For months, political analysts were projecting Democrats would pick up anywhere from four to seven Senate seats.
The outcome of the presidential race is expected to have a major impact on the outcome of the congressional campaigns, with a handful of Senate races at center stage.
One features Missouri Secretary of State Jason Kander, who is giving Republican Senator Roy Blunt a stiff challenge. Another is former environmental official Katie McGinty's bid to unseat Republican Senator Pat Toomey in Pennsylvania.
The Senate that will be sworn in on Jan. 3 will face weighty issues, such as filling a vacancy on the U.S. Supreme Court, immigration and free-trade deals with Pacific Rim countries and Europe.
(Editing by Kevin Drawbaugh and Peter Cooney)
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