US News & World Report:

Gay marriage opponents predict President Barack Obama's public endorsement of same-sex marriage will hurt his re-election chances and pledge to push the issue in key swing states. Officials at the National Organization for Marriage, a political group that helps fund state-based campaigns against gay marriage, had already denounced the president's position and said Tuesday they are confident their efforts will help ensure a victory for Republican nominee Mitt Romney.

"I believe that this will lead to President Obama being a one-term president," said NOM president Brian Brown, during a call with reporters. "If you look at key swing states—Ohio, Florida, North Carolina, Iowa—those are all states where you had overwhelming majorities vote to protect marriage, and I think that we are going to focus on making very clear that this is a key distinction obviously."

Ohio, Florida and most recently, North Carolina have all passed constitutional amendments banning same-sex marriage. While it's legal in Iowa via a court ruling, NOM counts votes to recall justices who supported its legalization as a sign from voters that they oppose it.

Brown pushed back against recent polling that shows Americans' views shifting rapidly in favor of same-sex marriage, claiming they often used 'biased' polling questions. He also pointed to the fact that despite any polling, each of the states that have had popular votes on same-sex marriage have seen voters come out against it. Gay marriage is legal in six states, either through court rulings or by legislation.