Republicans have been getting in trouble for asserting this since at least 1988 -- but anti-abortion politicians keep hauling out this old idea for a reason.

Here we go again. Trotting out the contemporary equivalent of the early American belief that only witches float, Rep. Todd Akin, the Republican challenger to Democratic U.S. Senator Claire McCaskill, told a local Missouri station in an interview that "legitimate rape" does not lead to pregnancy.

"First of all, from what I understand from doctors [pregnancy from rape] is really rare," Akin said in an interview with KTVI-TV that caused a furor online Sunday afternoon after being posted on TPM. "If it's a legitimate rape, the female body has ways to try to shut that whole thing down."

Akin's comments came during a discussion of his hardline stand against permitting legal abortions for rape victims. "I think there should be some punishment, but the punishment ought to be on the rapist and not attacking the child," he said.

McCaskill quickly rebuked him -- "As a woman & former prosecutor who handled 100s of rape cases, I'm stunned by Rep. Akin's comments about victims this AM," she tweeted -- and Republican operatives on Twitter joined in the chorus decrying his remarks and speculating that he would need to be pulled from the race if the GOP wanted to continue to have any shot at taking her seat. Akin, who had been leading in polls, issued a lengthy statement explaining that he "misspoke."