Ben Smith at Politico was first to take note:

Former Gov. Mitt Romney has joined Rep. Michele Bachmann and former Sen. Rick Santorum in signing a pledge to oppose same-sex marriage on a number of specific fronts.

... The pledge is less meaningful for its direct consequences than for the fact that it commits the three candidates fully to the hottest front in the culture wars.

Danny Yadron at the Wall Street Journal's Washington Wire blog:

Former Massachusetts Gov. Mitt Romney, Rep. Michele Bachmann (R., Minn.) and former U.S. Sen. Rick Santorum have signed a pledge from the National Organization for Marriage to oppose gay marriage at several levels of the federal government.

But former Minnesota Gov. Tim Pawlenty, who has sought to burnish his credentials as an evangelical Christian, declined to sign it, possibly putting him at odds with the social conservatives he is trying to court in Iowa. The National Organization for Marriage is running a four-day Iowa bus tour leading up to the Aug. 13 straw poll in Ames.

Kathryn Lopez at National Review's The Corner blog:

I’ve sorta tired of pledges, but it does seem bizarre that Tim Pawlenty hasn’t signed onto the National Organization of Marriage’s marriage pledge. The pledge is straightforward. And Governor Pawlenty does come from Minnesota, which has been a ground zero for the marriage debate lately. Pawlenty knows this is not a mere rhetorical debate for primary times.

Alex Pappas at The Daily Caller:

Sources tell The Daily Caller that Herman Cain, Newt Gingrich, Jon Huntsman, Gary Johnson, Thad McCotter, Ron Paul and Tim Pawlenty all declined to sign the pledge.

“Marriage is an issue with an unbroken string of victories that unites Republicans,” said Brian Brown, president of the conservative marriage advocacy group, “and we’re pleased and honored the leading candidates in the race for the GOP nomination have spoken up for marriage.”

The organization added that “serious announced candidates for the GOP nomination” had the opportunity to sign its marriage pledge.

Brian Montopoli at CBSNews' Political Hotsheet blog:

Rep. Michele Bachmann and Rick Santorum also signed the pledge, though that's not much of a surprise: Both candidates have grounded their campaigns in part in strong social conservatism. Romney's decision is more interesting because he has largely tried to keep his focus on fiscal issues and declined to sign an earlier, more far-reaching "values" pledge from a conservative group in Iowa.

More outlets:

• Alicia Cohn at The Hill's blog briefing room
• Kheli Bouarrouj of the DC Examiner
• Catalina Carnia at USA Today's On Politics blog
• Lynda Waddington at the Iowa Independent
• David Weigel at Slate
• Christian Broadcasting Network
• Huffington Post's HuffPost Hill Update
• Seattle Post Intelligencer Politics News blog
• Boston Globe's Political Intelligence blog
• International Business Times
• RTTNews
• Human Events