Brown has been endorsed by groups that both support and oppose abortion rights. The New York Times examined his voting record on abortion earlier this year and found he voted for measures such as the Blunt Amendment, which would have allowed employers to refuse to pay for certain health benefits, including contraception, if they opposed them on religious grounds.
Asked if he wants Mourdock to win, Brown replied that "It's up to the people of Indiana, certainly."
He and Warren are both vying for female voters, who could prove pivotal in the Senate contest.
The Mourdock controversy has drawn comparisons to Rep. Todd Akin's (R-Mo.) remark that victims of "legitimate rape" rarely become pregnant. Brown was one of the first senators to call on Akin to end his Senate bid. Akin later apologized and is continuing his run against Sen. Claire McCaskill (D-Mo.).
The latest WBUR poll found Warren leading Brown by five points. The survey had a 4.4 percentage point margin of error.
— This post was updated at 3:44 p.m.