Fearing a likely election victory is now in doubt, Republican leaders and candidates on Monday called on Missouri Rep. Todd Akin to abandon his bid for a crucial Senate seat because of his suggestion that women's bodies can avert pregnancies in cases of "legitimate rape.''

Mr. Akin had been running ahead in polls of Democratic Sen. Claire McCaskill, who is widely considered the most endangered Senate incumbent. But were he to lose, the GOP's chances of recapturing a majority in the Senate and enacting a sweeping conservative...