The president was applauded for his stand as he delivered a commencement address at New York's Barnard College Monday.
It's not an issue Republican Mitt Romney wants to talk about, but right now it's unavoidable.
Over the weekend Romney delighted Christian fundamentalists at Liberty University by defining marriage as "a relationship between one man and one woman".
Romney would rather talk economy, and what Republicans calls the president's out-of-control spending and debt.
The Obama campaign, meanwhile, is picking up the primary season attacks on Romney and his time at Bain Capital.
Team Romney is firing back with a new ad saying he and Bain were job creators, not job killers.
Meanwhile, the Republican primary season reached an unofficial end Monday when Ron Paul announced he was suspending his active campaign efforts.