Hey, who would have dreamed that Mitt Romney could use evolution to unite the social-conservative base?  Thanks to Barack Obama’s “evolution” on same-sex marriage, and Romney’s declaration that he will remain unmoved on the topic, social conservatives who had heretofore pledged to remain on the sidelines are now suiting up for November:

Social conservatives who doubted Mitt Romney now have a reason to rally around him after President Barack Obama’s embrace of gay marriage.

Despite the fact that very conservative and religious voters didn’t support Romney in the primary, their fierce opposition to the issue will give the presumptive GOP nominee a way to harness conservative enthusiasm in November.

And for Romney, whose position on same-sex marriage has been consistent over the years, conservative activists say Obama’s declaration may be a way for Romney to finally prove his bona fides to voters on the right who have always been suspicious that he’s not one of them.

“President Obama just ‘evolved’ himself into a one-term president,” said Brian Brown, the president of the National Organization for Marriage. “This is a disaster for the Democratic Party: The reality is that the exact states he needs to win are the states that have overwhelmingly passed legislation defining marriage as between a man and a woman.”

“What I’m hearing from folks around the country is: ‘Game on, we’re in, we will do whatever is necessary to elect Mitt Romney now because Obama has shown where he really stands,’” Brown said.

It’s difficult to know just how much this will help Romney.  Part of the problem in discerning that is calculating just how disaffected evangelicals and social conservatives would have really been in the general election.  It may be difficult to imagine millions of them sitting on their hands when given the opportunity to vote Obama out of office, but at least a few activist groups have threatened to do so unless Romney engaged in some explicit ring-kissing to their agendas.  Obama’s announcement this week might have taken all of that off the table and repositioned their thinking about Romney as no longer not reliable enough, but now a much better option in contrast to the status quo. Best of all, that doesn’t require Romney to actively adopt those agendas and potentially alienate social moderates.

This hot-button issue might provide even more than simple motivation to cast votes.  With this attack on traditional values, it seems inevitable now that social-conservative groups will unlock their wallets and checkbooks in an effort to fight Obama over the next five-plus months.  Put that on top of the battle that Catholic bishops are now fighting with Obama in the parishes over the HHS mandate on contraception and sterilization and we may see the largest faith-based mobilization and alliance ever in a presidential election.

For that reason, I’d guess that Obama will try to find his way to an accommodation with the USCCB over the HHS mandate.  I’m still surprised he hasn’t done so already to defuse the anger among Catholics who voted for him in 2008, but now he can’t afford to fight both the Catholics and a newly-mobilized evangelical movement.  Otherwise, the next evolution will be, as Brown says, a transition from Obama to Romney in January.