When Mitt Romney, candidate for president, came to the Conservative Political Action Conference in 2007, he was a fresh-faced over-eager student of Republican politics: He won cheers for a newfound social conservatism, and won a straw poll amid charges he’d packed the hall. Romney ended his candidacy in an emotional speech to CPAC the next year, and in 2009 he used the forum to open a critique of President Barack Obama that he spent the next year refining. The new Romney, received Thursday as the favorite son at the gathering of conservative activists, is a more constant, seasoned, and comfortable...