No wonder Missouri Senator Claire McCaskill wanted to run against Rep. Todd Akin, even investing in his GOP primary victory two weeks ago by spending $2 million on ads that described him as “too conservative.’’ Missouri Republicans saw that as a plus, just as she’d hoped. But after his Sunday comment that “legitimate rape” rarely leads to pregnancy, even some in the GOP are calling for him to step aside.

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The Republican lawmaker was trying to explain why he opposes abortion in cases of rape, but instead marched straight into the tar pits, where he will hopefully serve as a warning to future candidates that the reproductive info gleaned at summer camp may not hold up that well in TV interviews half a century hence.

Pregnancy as a result of sex by force “is really rare,” Akin told KTVI-TV. “If it’s a legitimate rape, the female body has ways to try to shut that whole thing down.”

Back up: Did this former engineer and father of six, who sits on the House Committee on Science, Space and Technology, just suggest that some rapes are not so legit? Yes, and that scary and powerful as women are, we have ways to avoid conceiving with rapists.

I wish that were the case. But as much as I like the gangster touch — we have ways — the American Journal of Obstetrics and Gynecology says otherwise. Based on a 1996 study, it estimates that about 5 percent of rape victims of child-bearing age do become pregnant as a result, in some 32,000 cases a year. This 2005 study found that 20 percent of 148 women seeking protective orders against abusive former partners had become pregnant as the result of a rape.

Akin does allow for a Plan B, so to speak: “But let’s assume that maybe that didn’t work or something,’’ he said, and a woman did become pregnant following a rape. “I think there should be some punishment, but the punishment ought to be on the rapist and not attacking the child.”

Later on Sunday, with McCaskill tweeting about her history as a prosecutor and Republicans running for cover, Mitt Romney’s campaign said, “Todd who?” (“Governor Romney and Congressman Ryan disagree with Mr. Akin’s statement,’’ their statement said, “and a Romney-Ryan administration would not oppose abortion in instances of rape.”)

Sen. Claire McCaskill, D-Mo. on Capitol Hill last year. Her opponent is Rep. Todd Akin, a tea party favorite who was endorsed in the primary by former Arkansas Gov. Mike Huckabee. (Manuel Balce Ceneta/AP)

Akin isn’t the first abortion opponent with retro rape views; earlier this year, Idaho state senator Chuck Winder said he hoped doctors were interrogating women seeking abortions following a rape to make sure they really had been violated.

Unsuccessful Republican Colorado Senate candidate Ken Buck, who lost to Michael Bennet in 2010, once suggested to a victim whose case he declined to prosecute that a “jury could very well conclude that this is a case of buyer’s remorse.”

With comments like these, no wonder so much of America remains convinced that only women-haters have abortion qualms; though Lord knows I don’t share that view, you guys aren’t helping, and should either read up or keep still.

Meanwhile — and I’m guessing we’ve got nothing but time — if Akin doesn’t get out of the race, he’s likely to wind up like Claytie Williams, whose 1990 remark comparing bad weather to rape (“If it’s inevitable, you might as well lie back and enjoy it”) made it possible for Ann Richards to become the first female governor of Texas since Ma Ferguson.