Roy Moore, the Republican nominee for a Senate seat in Alabama, spoke in Birmingham on Saturday. He has called the allegations against him “a desperate political attack.”

Allegations that Roy S. Moore, the Republican nominee for a Senate seat in Alabama, pursued sexual and romantic relationships with teenagers while he was in his 30s have upended a race in a state that has not had a Democratic senator since 1997.

While Alabama Republicans, by and large, defended Mr. Moore against what many of them described as a partisan plot, national officials have reacted with shock and disgust. And the shift away from him has been particularly pronounced in the chamber he hopes to join.

The National Republican Senate Committee is no longer raising money for Mr. Moore, and most Republican senators say he should end his campaign if the allegations — reported by The Washington Post on Thursday and based on more than 30 sources, including four accusers quoted by name — are true.

Here is a roundup of how the Senate’s 52 Republicans have responded.

Senator John McCain of Arizona called the allegations against Mr. Moore “deeply disturbing and disqualifying.”

Four senators — John McCain of Arizona, Bill Cassidy of Louisiana, Steve Daines of Montana and Mike Lee of Utah — unequivocally renounced Mr. Moore.

Mr. McCain was the first, tweeting on Thursday that Mr. Moore should step aside.

Mr. Lee tweeted on Friday, “Having read the detailed description of the incidents, as well as the response from Judge Moore and his campaign, I can no longer endorse his candidacy for the US Senate.” Mr. Daines and Mr. Cassidy quickly followed.

A fifth senator, Bob Corker of Tennessee, wrote that Mr. Moore should never have been nominated to begin with.

Senator John Cornyn of Texas, the majority whip, said that Mr. Moore’s candidacy would be unsustainable if the allegations were true, but that “we believe in a presumption of innocence until proven guilty.”

By far the most common reaction has been a call for Mr. Moore to step aside if the…