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John Locher, Associated Press
Senate Minority Leader Harry Reid of Nev., votes at an early voting site Wednesday, Oct. 26, 2016, in Las Vegas. When Sen. Harry Reid cast the last vote he’ll make as a U.S. Senator, he did it in a Las Vegas Strip early voting site surrounded by casino workers in the Culinary Union.

WASHINGTON — Republicans were all but guaranteed to keep their majority in the Senate Wednesday as they racked up key wins in Pennsylvania, Wisconsin, North Carolina, Indiana and Florida.

In Missouri, Democrat Jason Kander conceded to incumbent GOP Sen. Roy Blunt, eliminating Democrats' paths to Senate control. Republicans were expected to win an outstanding race in Alaska and a December runoff in Louisiana.

The outcome added to what was shaping up as a grim election night for Democrats, who face being consigned to minority status on Capitol Hill for years to come.

In Pennsylvania, GOP Sen. Pat Toomey won a narrow victory for his second term over Democratic challenger Katie McGinty. It was a race Democrats expected to win going into the night — and one that many Republicans felt nearly as sure they'd lose.

The story was the same in Wisconsin, where GOP Sen. Ron Johnson, written off for months by his own party, won re-election against former Democratic Sen. Russ Feingold in a rematch.

The race in GOP-held New Hampshire was too close to call, but even if Democrats won it they would be short of the seats needed to topple Republicans' 54-46 majority.

Republicans celebrated their wins, already looking ahead to midterms in 2018 when Democrats could see their numbers reduced even further with a group of red-state Senate Democrats on the ballot.

"We ran targeted, data-driven campaigns and communicated directly with voters. Those efforts paid off," said GOP Sen. Roger Wicker of Mississippi, head of the Senate GOP's campaign arm. "With the map strongly favoring Democrats and uncertainty at the top of the ticket, we protected our majority and paved the way for a Republican-run Senate for years to come."

Democrats grabbed a Republican-held seat in Illinois, where GOP Sen. Mark Kirk lost to Democratic Rep. Tammy Duckworth, a double-amputee Iraq war vet. That stood as the one Democratic pickup as Wednesday got under way.

The other bright spot for Democrats was in Nevada, where Minority Leader Harry Reid's retirement after five terms created a vacancy and the one Democratic-held seat that was closely contested. Reid maneuvered to fill it with his hand-picked successor, Catherine Cortez Masto, Nevada's former attorney general who spoke often of her family's immigrant roots in a state with heavy Latino turnout.

Cortez Masto will become the first Latina U.S. senator. She beat Republican Rep. Joe Heck, who struggled with sharing the ticket with Donald Trump, first endorsing and then un-endorsing Trump to the disgust of some GOP voters.

As the night wore on, Democratic operatives struggled to explain why their optimistic assessments of retaking Senate control were so mistaken. Some blamed unexpected turnout by certain segments of white voters, or FBI Director James Comey's bombshell announcement that he was reviewing a new batch of emails connected with Democrat Hillary Clinton.

In North Carolina, Democrats had high hopes of unseating entrenched GOP incumbent Sen. Richard Burr, who infuriated even his own party with his laid back campaign style. But in the end he had little trouble holding off a challenge from Democrat Deborah Ross. In Indiana, GOP Rep. Todd Young beat former Democratic senator and governor Evan Bayh, who mounted a much-ballyhooed comeback bid, but wilted under scrutiny.

And in Florida, GOP Sen. Marco Rubio beat Democratic Rep. Patrick Murphy, giving Rubio a platform from which he could mount another bid for president in 2020.

In Arizona, meanwhile, GOP Sen. John McCain, at age 80, won his sixth term in quite possibly his final campaign. The 2008 GOP presidential nominee was re-elected without much difficulty despite early predictions of a competitive race, and struck a reflective note ahead of the outcome.

"While as Yogi Berra said, 'I hate to make predictions, especially about the future,' I'm not sure how many more I have in me," McCain said.

In New York, Sen. Chuck Schumer, the Democrats' leader-in-waiting for a new Congress, easily won re-election. But the results elsewhere meant he would be leading a Senate minority when he replaces Reid in the leader's role.

The Senate races were shadowed every step of the way by the polarizing presidential race between Clinton and Republican Donald Trump. Yet in the end, Trump was apparently not the drag on GOP candidates widely anticipated, even though some Republicans struggled with sharing the ballot with him.

Even though the GOP's renewed control of the Senate is likely to be narrow, the advantages of being in the majority are significant. The controlling party holds the committee chairmanships, sets the legislative agenda and runs investigations. First up is likely to be a nominee to fill the vacancy on the Supreme Court.

Associated Press writer Mary Clare Jalonick contributed to this report.