Obama talks same-sex marriage on "The View" May 15, 2012 -- Updated 0824 GMT (1624 HKT) Poll: 51% of Americans approve of President Obama's support for gay marriage This issue is going to be a big contrast in the 2012 campaign, Obama says Romney says marriage should be between a man and a woman This is Obama's fourth appearance on "The View" (CNN) -- Last week, Barack Obama went on record as the first American president to support same-sex marriage, but he doesn't appear ready to take his commitment beyond the endorsement stage. In an interview scheduled to air Tuesday on ABC's "The View," Obama wouldn't commit to fighting for the the repeal of the Defense of Marriage Act (DOMA) -- a federal law that defines marriage as the legal union between one man and one woman. "My justice department has said to the courts, we don't think the Defense of Marriage Act is constitutional," the president said in advance excerpts released by the network. This is something that historically had been determined at the state level and part of my believing ultimately that civil unions weren't sufficient. But pressed further if he would fight to repeal DOMA, Obama would only say, "Congress is clearly on notice that I think it's a bad idea." More than 30 states have voted in favor of constitutional amendments that defend the traditional definition of marriage as a heterosexual union. The president does see the issue looming large in the 2012 election. "This is going to be a big contrast in the campaign, because you've got Gov. (Mitt) Romney saying we should actually have a constitutional amendment installing the notion that you can't have same-sex marriages," Obama said in the interview recorded Monday. Last week, Romney reaffirmed his position on gay marriage, saying marriage "should be a relationship between a man and a woman." "Let me make it very clear, that my preference is to have a national standard that defines marriage as a relationship between a man and a woman," Romney said. That would then allow states to determine what rights would be provided for people of the same gender that wanted to have a relationship. While 50% approve of same-sex marriage, a further breakdown of the numbers shows a significant gender gap: 56% of women say couples of the same gender should be legally allowed to marry, while 42% of men feel the same way. This is the Obama's fourth appearance on "The View" -- his second since taking up residence in the White House.