At a gay fundraiser on Saturday, President Barack Obama took his GOP rivals to task over the booing of a gay soldier.

During last month's televised Fox News/Google debate, presidential candidate Rick Santorum answered a question submitted by Stephen Hill, a gay soldier serving in Iraq.

Referring to the recent repeal of “Don't Ask, Don't Tell,” Hill, dressed in an Army t-shirt, asked via a YouTube clip: “Do you intend to circumvent the progress that has been made for gay and lesbian soldiers in the military?”

The audience booed Hill's question, but cheered Santorum when he called DADT repeal a “tragic social experiment” and vowed he would reinstate the policy, if elected president.

“We don't believe in the kind of smallness that says it's okay for a stage full of political leaders – one of whom could end up being the President of the United States – being silent when an American soldier is booed. We don't believe in that. We don't believe in them being silent since. You want to be commander-in-chief? You can start by standing up for the men and women who wear the uniform of the United States, even when it's not politically convenient,” Obama said.

Three of the candidates – former Pennsylvania Senator Rick Santorum, former Utah Governor Jon Huntsman and former New Mexico Governor Gary Johnson – condemned the booing in comments offered after the debate.

The president also reiterated his support for repeal of the Defense of Marriage Act (DOMA), the law that bans federal agencies from recognizing the legal marriages of gay and lesbian couples.

“I believe the law runs counter to the Constitution, and it's time for it to end once and for all,” he told the crowd.

(Related: Obama jokes he met with gay leader Lady Gaga at HRC fundraiser.)