WATCH: Fox Host Grills Santorum on Marriage

Rick Santorum, extolling the virtues of marriage, found an unexpectedly tough interviewer this week in Fox News's Neil Cavuto, who challenged him to address the benefits of marriage for same-sex couples.

The antigay former U.S. senator and Republican presidential aspirant, who was promoting his new book, Blue Collar Conservatives, told Cavuto, "I talk and actually spend a couple of chapters talking about the importance of the family unit for the economy." Even many a "liberal study," Santorum said, "has come out and shown that, gee, the most important factor as to whether people do well economically is whether they're in stable married relationships or not." Cavuto then asked, "Let's say if your mom and dad are the same sex, is that a stable environment?"

Santorum was evasive, saying the issue at hand should be "promoting the institution of marriage of men and women staying together and raising children." Cavuto continued to press him, but Santorum insisted, "I think we need to focus on the vast majority of the people who are going to be in man-and-woman relationships raising children."

Santorum, who says he's considering another presidential run in 2016, has been making the rounds lately. Last week he appeared on conservative talk-show host Lars Larson's radio program, where he said all the predictions he made in the wake of the Supreme Court's 2003 decision invalidating sodomy laws have come true. At the time, he predicted that a legal right to consensual gay sex would lead to rights to bigamy, polygamy, and incest.

"Despite Santorum's self-congratulatory remarks, bigamy, polygamy, and incest have not been legalized in the U.S., or in any of the states that have marriage equality laws for that matter," notes Right Wing Watch.

Watch Santorum's exchange with Cavuto and listen to his remarks to Larson below.