Republicans terrified Trump will cost them Congress: 'He'll drag the Senate and House down with him'
Paul Ryan, Donald Trump and Mitch McConnell

Republicans are despondent that Donald Trump threw away his third -- and final -- chance to win votes for himself and GOP congressional candidates at Wednesday night's presidential debate.

Trump appears increasingly unlikely to win the 270 electoral votes needed to gain the White House, but the party that nominated him is growing more concerned that they'll lose majorities in both the U.S. Senate and House, reported Politico.

“The biggest loser (Wednesday) was not Trump -- the presidential race is over,” said GOP pollster Robert Blizzard. “Instead, down-ticket Republicans lost tonight. They needed some help and got absolutely none.”

Sex assault allegations against Trump have damaged some other GOP candidates, according to the party's own polls, and Republicans had hoped their nominee might turn in a strong performance to assure voters of his qualifications and temperament.

Instead, Trump threatened to hold American democracy hostage if he didn't like the results of the Nov. 8 election.

“It’s the one and only headline that matters coming out of the debate,” said said GOP strategist Steve Schmidt. “It’s absolutely unprecedented for any presidential candidate in the history of the country.”

The remark, which echoed his frequent complaints about a "rigged election," overshadowed what some Republicans felt was his strongest debate performance.

“For him, that is a big takeaway from (Wednesday)," said GOP strategist Austin Barbour. It’s a shame for him, he could have walked away, I think, as the winner from (Wednesday), but that line will be one that is played in a big — in a bigly — way with the press (Thursday).”

With polls showing Trump is headed for a resounding loss, Republicans may start trying to salvage their congressional races by promising to serve as a "check and balance" against a likely Hillary Clinton presidency.

“Trump was already behind,” said Bill Kristol, a Trump critic and editor-in-chief of The Weekly Standard. “He didn't help himself (Wednesday), indeed he hurt himself. He's very likely to lose, and to lose badly. He'll drag the Senate and House down with him unless Senate and House candidates can make the case they're needed to check and balance Hillary.”