The delicate issue of pregnancies resulting from rape rattled another campaign for the Senate Tuesday when Indiana’s Republican Senate nominee, Richard Mourdock, said a life conceived by rape “is something that God intended to happen” and must be protected.

The comments came during a debate with Mr. Mourdock, the state treasurer; the Libertarian candidate Andrew Horning; and Representative Joe Donnelly, the Democrat locked in an unexpectedly tight contest for the seat now held by the Republican Senator Richard Lugar. All three were trying to distinguish themselves, since they all are identified as opposing abortion.

“I’ve struggled with it myself for a long time, but I came to realize that life is that gift from God,” Mr. Mourdock said. “And even when life begins in that horrible situation of rape, that it is something that God intended to happen.”

The comments echoed back to the Republican Senate nominee Todd Akin’s defense of his position opposing abortion in all instances. Mr. Akin, a Congressman from Missouri, said, “If it’s a legitimate rape, the female body has ways to try to shut that whole thing down.” That comment set off a firestorm, with Republicans and Democrats alike castigating Mr. Akin and Republicans pressuring him to leave his race against the Democratic Senator Claire McCaskill. Mr. Akin refused, and a seat once widely expected to go to the Republicans in November now could stay with the Democrats.

Democrats, who have waged a fierce campaign against Mr. Mourdock, labeling him a Tea Party extremist, hoped lightning had struck twice.

“I think rape is a heinous and violent crime in every instance,” Mr. Donnnelly said in a statement after the debate. “The God I believe in and the God I know most Hoosiers believe in, does not intend for rape to happen — ever. What Mr. Mourdock said is shocking, and it is stunning that he would be so disrespectful to survivors of rape.”

Mr. Donnelly, a Catholic, is also opposed to abortion. But the response forced Mr. Mourdock to backpedal.

“God creates life, and that was my point,” Mr. Mourdock said. “God does not want rape, and by no means was I suggesting that he does.”

The back and forth comes as Democrats — from President Obama on down — have tried to widen their advantage with female voters and play up the abortion issue. The Indiana Senate race is considered to be leaning Republican, but the state, which voted for Mr. Obama in 2008, is not in play this year. That was expected to give a slight edge to Mr. Mourdock, who defeated Mr. Lugar in a heated Republican primary.

Democrats quickly moved to capitalize on the controversy. The Democratic National Committee pointed to an advertisement that Mitt Romney cut for Mr. Mourdock, and asked whether the Republican presidential nominee would repudiate his endorsement.

“Richard Mourdock’s rape comments are outrageous and demeaning to women,” said Debbie Wasserman Schultz, the chairwoman of the Democratic National Committee. “Unfortunately, they’ve become part and parcel of the modern Republican Party’s platform toward women’s health, as Congressional Republicans like Paul Ryan have worked to outlaw all abortions and even narrow the definition of rape. As Mourdock’s most prominent booster and the star of Mourdock’s current campaign ads, Mitt Romney should immediately denounce these comments and request that the ad featuring him speaking directly to camera on Mourdock’s behalf be taken off the air.”