Rick Santorum finally offered a formal endorsement for presumptive GOP presidential nominee Mitt Romney late on Monday night. But it was hardly a ringing proclamation of approval for his former rival. From its timing (after 11 pm on the East Coast) to its form ( an email to supporters posted on his campaign website) to its language (more pointing out his differences with Romney than extolling Romney's virtues) it's a decidedly underwhelming nod to the man who bested him in the Republican primaries.