In a letter posted to his website last night, Rick Santorum offered a tepid endorsement of Mitt Romney.

Reads the letter, in part:

The primary campaign certainly made it clear that Governor Romney and I have some differences. But there are many significant areas in which we agree: the need for lower taxes, smaller government, and a reduction in out-of-control spending. We certainly agree that abortion is wrong and marriage should be between one man and one woman. I am also comfortable with Governor Romney on foreign policy matters, and we share the belief that we can never allow Iran to possess nuclear weapons. And while I had concerns about Governor Romney making a case as a candidate about fighting against Obamacare, I have no doubt if elected he will work with a Republican Congress to repeal it and replace it with a bottom up, patient, not government, driven system.

Above all else, we both agree that President Obama must be defeated. The task will not be easy. It will require all hands on deck if our nominee is to be victorious. Governor Romney will be that nominee and he has my endorsement and support to win this the most critical election of our lifetime.

Writes Joel Roberts at The Ticket:

From its timing (after 11 p.m. on the East Coast) to its form (an email to supporters posted on his campaign website) to its language (more highlighting his differences with Romney than extolling Romney's virtues) it's a decidedly lukewarm nod to the man who bested him in the Republican primaries.