A furious fight for control of the U.S. Congress being waged alongside the White House race between Democrat Hillary Clinton and Republican Donald Trump ends on Tuesday with elections that will help shape the country's policy decisions for the next two years.
At stake is Republicans' current grip on the Senate and House of Representatives. If voters hand power to Democrats in either chamber, 2017 will likely bring a more moderate bent to bills that lawmakers send to the new president for signing into law.
In order to win control of the Senate outright, 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 much of the autumn campaign, political analysts were projecting Democrats would pick up anywhere from four to seven Senate seats.
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The best of 2016 election t-shirts
The best of 2016 election t-shirts
An attendee stands for a photograph while wearing a shirt in support of Senator Bernie Sanders, an independent from Vermont and 2016 Democratic presidential candidate, not pictured, in Kenosha, Wisconsin, U.S., on Wednesday, March 30, 2016. After routing Hillary Clinton in three western-state Democratic caucuses, Sanders still faces daunting delegate math and a road ahead dominated by big-state primaries that have been the weakest link in his campaign. Photographer: Luke Sharrett/Bloomberg via Getty Images
A supporter wearing a t-shirt with US Republican presidential candidate Donald Trump attends a Trump rally at Liberty University in Lynchburg, Virginia, January 18, 2016. / AFP / NICHOLAS KAMM (Photo credit should read NICHOLAS KAMM/AFP/Getty Images)
An attendee poses with her homemade shirt during US Republican presidential candidate Donald Trump's campaign rally at the American Airlines Center in Dallas on September 14, 2015. AFP PHOTO/LAURA BUCKMAN (Photo credit should read LAURA BUCKMAN/AFP/Getty Images)
RICHMOND, VA - OCTOBER 14: A young woman wears a Donald Trump t-shirt as thousands of people line up at the Richmond International Raceway to get into a political rally with presidential candidate and Republican front-runner Donald Trump October 14, 2015 in Richmond, Virginia. A New York real estate mogul and reality television star, Trump is now in a statistical tie with retired neurosurgeon Ben Carson in a Fox News survey of likely Republican voters released Tuesday. (Photo by Chip Somodevilla/Getty Images)
ATLANTA, GA - FEBRUARY 29: A veteran in the audience shows his support for Republican presidential candidate Senator Marco Rubio (R-FL) during a campaign rally at the Intercontinental Buckhead Hotel in Atlanta, Ga., on February 29, 2016. (Photo by Jessica McGowan/Getty Images)
Attendees enter a campaign event for Senator Bernie Sanders, an independent from Vermont and 2016 Democratic presidential candidate, at the Colorado Convention Center in Denver, Colorado, U.S., on Saturday, Feb. 13, 2016. In the first Democratic debate on Thursday since her crushing defeat in New Hampshire, Hillary Clinton tried a new approach to win back wavering supporters, capturing Bernie Sanders anger without looking angry. Photographer: Matthew Staver/Bloomberg via Getty Images
A supporter of Senator Ted Cruz, a Republican from Texas and 2016 presidential candidate, shows off his T-shirt while watching caucus results on television during the Cruz campaign's caucus night celebration at the Elwell Center on the Iowa State Fairgrounds in Des Moines, Iowa, U.S., on Monday, Feb. 1, 2016. Cruz won the Iowa Republican caucuses in an upset over billionaire Donald Trump, while Democrat Hillary Clinton was clinging to the narrowest edge over Senator Bernie Sanders of Vermont. Photographer: Luke Sharrett/Bloomberg via Getty Images
FALLON, NV - FEBRUARY 23: Walter Hogan poses for a portrait after participating in the Republican caucus at the Churchill County Fairgrounds on February 23, 2016 in Fallon, Nevada. The remaining Republican presidential candidates are seeking support from voters in Nevada's 'first in the West' caucus. (Photo by David Calvert/Getty Images)
FAIRFIELD, AL - FEBRUARY 27: Supporters look on as Democratic presidential candidate former Secretary of State Hillary Clinton speaks during a 'Get Out The Vote' at Miles College on February 27, 2016 in Fairfield, Alabama. Hillary Clinton held a campaign rally in Alabama before returning to South Carolina for her South Carolina primary night event. (Photo by Justin Sullivan/Getty Images)
OVERLAND PARK, KS - MARCH 02: A child shows his family support of Republican presidential candidate, Sen. Ted Cruz (R-TX) while waiting in a line outside Yardley Hall at Johnson County Community College before a campaign rally ahead of caucuses on March 02, 2016 in Overland Park, Kansas. Cruz is coming off wins in Texas, Oklahoma and Alaska in yesterday's Super Tuesday. (Photo by Kyle Rivas/Getty Images)
UNITED STATES - JANUARY 26 - Mark Knauer, from Des Moines, Iowa, listens as he wears a shirt donning Democratic presidential candidate Sen. Bernie Sanders during a meeting with workers from the United Steelworkers Local 310L in Des Moines, Iowa, Tuesday, Jan. 26, 2016. (Photo By Al Drago/CQ Roll Call)
An attendee wears a campaign t-shirt for Donald Trump, president and chief executive of Trump Organization Inc. and 2016 Republican presidential candidate, during a Trump campaign rally at the Radford University Dedmon Arena in Radford, Virginia, U.S., on Monday, Feb. 29, 2016. The single biggest day of voting in the Republican primary is March 1, Super Tuesday, when nearly half of the delegates needed to secure the nomination are up for grabs with Trump favored in most of these contests. Photographer: Andrew Harrer/Bloomberg via Getty Images
An attendee wears a Senator Bernie Sanders, an independent from Vermont and 2016 Democratic presidential candidate, shirt during a campaign event in Exeter, New Hampshire, U.S., on Friday, Feb. 5, 2016. Democratic Party officials in Iowa say they can't do a recount of Monday's razor-thin presidential caucus results between Hillary Clinton and Sanders, even if they thought it was appropriate. And both candidates, in their debate later Thursday night, said it was no big deal. Photographer: Victor J. Blue/Bloomberg via Getty Images
HENDERSON, NV - FEBRUARY 19: Alex Leichenger canvasses a neighborhood for Democratic presidential candidate Sen. Bernie Sanders on February 19, 2016 in Henderson, Nevada. Sanders is challenging Hillary Clinton for the Democratic presidential nomination ahead of Nevada's February 20th Democratic caucus. (Photo by Ethan Miller/Getty Images)
An attendee wears a shirt in support of Donald Trump, president and chief executive of Trump Organization Inc. and 2016 Republican presidential candidate, not pictured, during a campaign rally at the Port Columbus International Airport in Columbus, Ohio, U.S., on Tuesday, March 1, 2016. State officials were reporting strong turnout for Super Tuesday balloting, the closest thing yet to a national referendum on Trump, the brash New York billionaire who has thrown out the traditional rules of campaigning. Photographer: Ty Wright/Bloomberg via Getty Images
DOVER, NH - FEBRUARY 3: Robert Hodgman wore a 'Hillary for Prison 2016' shirt during a Marco Rubio town hall event at Cara Irish Pub in Dover, N.H. on Feb. 3, 2015. (Photo by Craig F. Walker/The Boston Globe via Getty Images)
MIAMI, FL - SEPTEMBER 12: Republican presidential candidate and former Florida Governor Jeb Bush shows off a Reagan/Bush '84 tee-shirt as he speaks during a Miami field office opening on September 12, 2015 in Miami, Floria. Bush continues to campaign for the Republican nomination. (Photo by Joe Raedle/Getty Images)
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But Democrats worried that the FBI's disclosure in late October it was reviewing newly discovered emails to see if they pertained to Clinton's use of a private email server while secretary of state might tip some competitive races toward Republicans.
The FBI said on Sunday the agency had completed its review of the newly found emails and found no reason to change its July finding that no criminal charges were warranted against Clinton.
Democrats face a steeper challenge in the House, having to gain 30 seats to win back the majority they last held in 2010. Some analysts have been projecting Democrats could pick up anywhere from five to 20 seats.
TIGHT SENATE CONTESTS
Republican control of the 100-seat Senate over the past two years and the 435-seat House of Representatives since 2011 has brought a sustained assault against Democratic President Barack Obama's landmark healthcare law known as Obamacare.
House Republicans have halted progress made in the Senate in 2013 on comprehensive immigration reform and Republicans have generally pushed for rolling back spending on domestic programs while trying to limit environmental and financial industry regulation.
The outcome of the presidential race is expected to have a major impact on the outcome of the congressional campaigns. In recent decades, the party that wins the White House has usually fared better in congressional races too.
For most of the 2016 campaign season, the Senate races have been center-stage, as Democrats fielded some strong challengers to Republican incumbents.
Among them are Missouri Secretary of State Jason Kander, who is giving Republican Senator Roy Blunt an unexpectedly stiff challenge, and former environmental official Katie McGinty, who could unseat Republican Senator Pat Toomey in Pennsylvania.
John McCain, the Vietnam War hero and 2008 Republican presidential nominee who has served in the Senate for 30 years appears headed to re-election in a race that has been unusually competitive for him.
A possible 50-50 tie following Tuesday's elections would mean that the next vice president would cast the tiebreaking vote and determine which party controls the Senate.
The Senate that will be sworn in on Jan. 3, whether it is held by Republicans or Democrats, will face a weighty decision early on - voting on a U.S. Supreme Court justice to replace the conservative Justice Antonin Scalia who died last February.
Since that time, Senate Republicans have refused to consider Obama's nomination of federal judge Merrick Garland, arguing the next president should pick a nominee for Senate review.
Other issues confronting Congress next year include the need to raise U.S. borrowing authority, something some conservative Republicans oppose without substantial budget cuts, and possible approval of free-trade deals with Pacific Rim countries and Europe if negotiations on the latter conclude successfully.
(Reporting by Richard Cowan; Editing by Kevin Drawbaugh and Peter Cooney)