Republican presidential candidate Rick Santorum says the end of the military's "don't ask, don't tell" policy that barred gays and lesbians from serving openly is a social experiment pushed by Democrats.

Santorum on Thursday said the military has one responsibility: protecting the country. He says that allowing gays and lesbians to serve openly is a distraction to that role.

The former senator from Pennsylvania was responding to a video question from a gay soldier that yielded boos from the debate audience. Congress repealed the Clinton-era ban; it ended Tuesday.

Santorum says that "sex is not an issue" and the government should leave it alone. He also says he would not expel the soldier who asked the question.