Mr. McConnell’s leadership does not appear to be in jeopardy. Aides to Mr. McConnell say he has already secured enough votes for his re-election as leader, regardless of the November results. And supporters say such threats have surfaced in the past, only to fizzle after Election Day.

Rand Paul of Kentucky made headlines in 2010 while running for the Senate when he declined to say whether he would back Mr. McConnell for leader after Mr. McConnell supported another Republican in the primary. Ultimately, Mr. McConnell was unanimously re-elected as leader, and his standing has remained solid among Senate Republicans even as he has faced sniping from some on the right who say he is too much of a Washington insider.

Mr. McConnell evinced no concern.

“In November, if the American people give us the ability to set the agenda in the Senate, I’m confident our conference will have broad unity around our efforts to repeal Obamacare, reduce the size and scope of government, and prevent job-killing tax hikes,” he said in a statement.

Mr. McConnell has already made adjustments. He recently enlisted Senator Ron Johnson of Wisconsin, a freshman elected with Tea Party backing, to lead efforts to coordinate the Republican messages and agenda in the Senate and the House with the party’s presidential nominee. A spokesman for Mr. McConnell, Don Stewart, said Mr. McConnell was exploring joining Mr. Mourdock on the campaign trail.

But pressure remains. Several Republican freshmen in the Senate — among them Mr. Paul, Mr. Johnson, Mike Lee of Utah and Marco Rubio of Florida — under the tutelage of the Tea Party kingmaker Jim DeMint of South Carolina, have laid the groundwork for a more conservative path in the Senate, often throwing their own logs on the fire of gridlock that has seized Congress.

The stakes are considerable. The country faces what the Federal Reserve chairman, Ben S. Bernanke, has called a “fiscal cliff” on Jan. 1, when the Bush-era tax cuts of 2001 and 2003 are set to expire and across-the-board spending cuts of more than $1 trillion are to go into effect. If a bipartisan agreement cannot be reached before the end of the year, nearly $8 trillion in deficit reduction could go into force in a sudden rush, a boon to budget hawks but a potential disaster for the fragile economic recovery.

After the election, the losing party is more likely to limp back to a lame-duck session of Congress aggrieved at its perceived mistreatment, and the winners will feel more empowered.