Akin said Thursday that McCaskill's demeanor during last week's debate differed vastly from her 2006 campaign against Jim Talent, which he contends demonstrates she thinks he's going to win this fall.
"I think we have a very clear path to victory, and apparently Claire McCaskill thinks we do, too, because she was very aggressive at the debate, which was quite different than it was when she ran against Jim Talent," Akin said at a news conference in the state Capitol. "She had a confidence and was much more ladylike (in 2006), but in the debate on Friday she came out swinging, and I think that's because she feels threatened."
The comments -- which come a little more than a month after his campaign was nearly derailed after claiming during a TV interview that victims of "legitimate" rape have a biological ability to ward off pregnancy -- reverberated around the Internet and drew an immediate rebuke from Democrats.
U.S. Sen. Patty Murray, chairwoman of the Democratic Senatorial Campaign Committee, said Akin's comments were "demeaning to women and offensive to all" and she called on national Republicans to repudiate them.
Jackson County Legislator Crystal Williams, a Democrat, said, "It's insulting beyond belief, particularly since it is coming from a man who has so little knowledge and understanding of women's lives."
Ryan Hite, Akin's press secretary, said the campaign had no comment. McCaskill's campaign could not immediately be reached for comment.
During their first face-to-face showdown at a debate sponsored by the Missouri Press Association, McCaskill wasted no time going after Akin, using her opening statement to paint a picture of the six-term Republican congressman as a political extremist who is "so far on the fringe."
But on Thursday, Akin said it was McCaskill whose views do not fall in line with the majority of Missourians.
"She's out of step badly with the state of Missouri," Akin said, later adding: "Her voting record just doesn't fit."
Following his remarks on rape last month, Republican leaders in Missouri and nationally joined together to call on Akin to drop out of the race. If he did not, they pledged that they would not support him with money or resources, despite the fact that most predict Republicans would be hard pressed to regain control of the Senate without Missouri's seat.
This week, however, the deadline for dropping out passed and many of those same Republican leaders switched course and publicly declared their support for Akin.
The National Republican Senatorial Committee, which could funnel millions of campaign dollars into the Show-Me State, hinted earlier this week that it might jump into the race on Akin's behalf. A spokesman for the committee said Thursday it would have no comment on Akin's latest remarks.
But Sen. John Cornyn of Texas, the chairman of the committee, said Thursday that he does not intend to put money into the Akin race.
"We have no plans to do so," Cornyn told The Louisville Courier-Journal in an interview. "I just think that this is not a winnable race. ... We have to make tough calculations based on limited resources and where to allocate it, where it will have the best likelihood of electing a Republican senator."
However, the Senate Conservatives Fund, a political action committee associated with South Carolina Sen. Jim DeMint, announced Thursday that it was pledging $290,000 in support of Akin.
One Republican who has refused to jump on the Akin bandwagon is former Republican U.S. Sen. John Danforth of St. Louis. He said earlier this week that Akin has tainted the GOP's brand and alienated women.
"He has become the type of somebody who has just been totally written off by women, and I think that's the problem," Danforth told the online news site PoliticMO.
Meanwhile, women's groups and unions are lining up in opposition to Akin.
Women Vote!, the independent expenditure arm of EMILY's List, a group that supports pro-choice women Democratic candidates, and the Service Employees International Union, announced a $1 million buy in Missouri to run campaign ads against Akin.
For his part, Akin last week launched a "Women for Akin" group in an effort to appeal to women voters.
Despite those efforts, Thursday's comments appeared to bring the women's issue back to the forefront.
"I'd like to know what his definition of 'ladylike' is, because we know his definition of rape is incorrect," said Barb Womack, chairwoman of the Missouri State Women's Political Caucus. "Women will remember in November. Trust me."
At his news conference, Akin insisted he will still win on Nov. 6.
"Here comes a voter into the voting booth and he's voting for (Mitt) Romney," he said. "Is he going to cross over and vote for Claire McCaskill? I don't think so. That doesn't make any sense at all."