Rick Santorum (Getty)

If Rick Santorum becomes President, he plans to pass a federal Constitutional amendment banning gay marriages that would invalidate marriage licenses that have been issued to couples in the states where same sex weddings are currently legal. Mr. Santorum outlined his position on gay marriage during the Republican presidential debate tonight in Manchester, New Hampshire.

"I believe the issue of marriage itself is a federal issue, that we can't have different laws with respect to marriage, we have to have one law," Mr. Santorum said. "Marriage is ... a foundational institution of our country and we have to have a singular law with respect to that, we can't have somebody married in one state and not married in another."

Mr. Santorum envisions that couples married under current state laws would not be grandfathered in under this Constitutional amendment and would have their weddings invalidated.

"If the Constitution says marriage is between a man and a woman, then marriage is between a man and a woman, and therefore, that's what marriage is and would be in this country," Mr. Santorum said. "And those who are not men and women who were married would not be married, as the Constitution would say."

Throughout his career, Mr. Santorum has been a prominent opponent of gay rights. Approximately 130,000 same sex couples reported being married in the 2010 U.S. Census.