Remarks by Richard Mourdock of Indiana and Todd Akin of Missouri may have seriously damaged their campaigns, The Hill reported Friday.
Mourdock had previously been set back by gaffes when he said at a Tuesday night debate that pregnancy caused by rape was something "God intended to happen," the report said.
Mourdock later said he meant "God creates life."
Democrats have used earlier verbal missteps by Mourdock, such as saying the "highlight of politics" was being able to "inflict my opinion on someone else," to paint him as an extremist.
Akin created a similar flap when he said that "legitimate rape" rarely leads to pregnancy.
The comments have "the potential to cost the party control of the Senate," said Republican strategist Ford O'Connell.
Republicans can get control of the Senate by winning just a few seats: four if President Obama wins and three if challenger Mitt Romney wins (because the vice president casts the tie-breaking vote).