Republicans retained control of Capitol Hill as Democrats managed to flip only two Senate seats in Illinois and New Hampshire.
On Wednesday, Republican Kelly Ayotte conceded her New Hampshire seat to Gov. Maggie Hassan, NBC News reported. The two candidates were separated by a few hundred votes in the state Wednesday afternoon.
Republican incumbent Pat Toomey was the apparent winner in Pennsylvania, NBC News projected. The GOP senator defeated Democrat Katie McGinty in what was the most expensive race ever for a Senate seat.
Republican Sen. Ron Johnson was the likely winner in Wisconsin, NBC News projected. The result was a surprise as Democrat Russ Feingold led Johnson by 2.7 points ahead of the election, according to a RealClearPolitics average.
GOP incumbent Roy Blunt also kept his seat in Missouri, NBC News projected, defeating Democrat Jason Kander.
Republican Todd Young was projected to win a Senate seat in Indiana, according to NBC News.
The retirement of Republican Sen. Daniel Coats opened the field in Indiana, traditionally a red state. As voters headed to the polls, Young was leading the contest by only 0.7, according to a RealClearPolitics average of recent polls.
Democrat Evan Bayh, a former senator and governor, was initially expected to trounce Young by double digits. His lead crumbled amid Republican attacks that characterized Bayh as a self-interested politician who had become disconnected from the people of Indiana.
In Illinois, Democratic congresswoman Tammy Duckworth was projected to win, according to NBC News, ousting incumbent Republican Sen. Mark Kirk. Democrats were also able to keep retiring Sen. Harry Reid's Nevada Senate seat as Catherine Cortez Masto beat Republican challenger Joe Heck, NBC News projected.
Cortez Masto's victory also makes history as she will become the first Latina U.S. senator.
NBC News projected that GOP incumbent Richard Burr will hold onto his seat in North Carolina, fighting off Democrat Deborah Ross. Republican Sen. John McCain was projected to keep his Arizona seat as expected, according to NBC News.
NBC News projected that California Attorney General Kamala Harris defeated fellow Democrat Loretta Sanchez in the Golden State's Senate race. Under California law, the top two vote-getters in the primaries face off in the general election, even if they're in the same party.
Democrats Ron Wyden and Brian Schatz were projected to win in Oregon and Hawaii, respectively, according to NBC News. Democrat Patty Murray and Republican Mike Crapo were projected to win their races in Washington and Idaho, respectively, according to NBC News.
In Louisiana, no candidate has met the required threshold to win the Senate race. Republican John Kennedy and Democrat Foster Campbell will advance to a runoff for the state's Senate seat.
Markets were hoping for continued gridlock between the White House and Congress, which would mean a continuation of the status quo, dampening potential volatility. In particular, markets will be sensitive to the Senate since the GOP was expected to hold onto the House.
Had Hillary Clinton won the presidency, the Democrats needed to win four seats to snatch control of the Senate since her vice president, Tim Kaine, would be the tie-breaking vote. They needed five seats in the event of her loss.
Control of the Senate could be crucial in determining the fate of major legislation, including the Dodd-Frank banking regulations and the Consumer Financial Protection Bureau.
Correction: This story was revised to correct that Sen. Patty Murray of Washington is a Democrat.