“I don’t see how they’ll avoid getting in the race,” he added.

But Republicans should focus on more than the Senate math, said John C. Danforth, a former Republican senator from Missouri who quickly distanced himself from Mr. Akin after the comments in August.

“Akin has come to symbolize a version of the Republican Party that’s just not acceptable to an awful lot of people,” Mr. Danforth said in an interview. “I don’t know if he can win or not in the election in the Senate race, but I think this is bigger than one Senate seat. I think it’s the brand of the Republican Party, and I think he taints the Republican Party.”

While Mr. Danforth is maintaining his opposition to Mr. Akin, other Republicans are returning to his corner. Senator Roy Blunt of Missouri and two former senators from the state, Christopher S. Bond and Jim Talent, recently endorsed Mr. Akin after initially urging him to step aside after his comments about rape and abortion.

“They’re going to have to explain to voters whether they support his position on these issues or whether they’re just acting in political expediency,” said Caitlin Legacki, a spokeswoman for Ms. McCaskill.

Mr. Blunt declined a request for an interview. But in a statement released shortly after the Sept. 25 deadline for dropping out of the race, he gave Mr. Akin an endorsement that sounded more obligatory than excited.

“Congressman Akin and I don’t agree on everything, but he and I agree the Senate majority must change,” Mr. Blunt said. “From Governor Romney to the county courthouse, I’ll be working for the Republican ticket in Missouri, and that includes Todd Akin.”