US Congressman Todd Akin (Republican), who caused outrage with a comment about rape, says he will not drop out of an election for a Senate seat.
Mr Akin, a six-term congressman, is challenging Senator Claire McCaskill (Democratic) of Missouri for her seat.
But his campaign turned controversial after he said in a television interview on Sunday that women have biological defences to prevent pregnancy in cases of what "legitimate" rape, making legal abortion rights unnecessary.
Both President Barack Obama and his Republican rival Mitt Romney have condemned the comments.