CNN says so, citing this quote from John McCain as evidence that he's warming toward Romney as a runningmate:
"I'm appreciative every time I see Mitt on television on my behalf," McCain said at a fundraising event in New Mexico. "He does a better job for me than he did for himself, as a matter of fact." [Emphasis added.]
But isn't that last bit actually a bit of a putdown? It's not like McCain said, "He does a better job than I do, as a matter of fact." One of the biggest factors in Romney's veep prospects is whether McCain can overcome the dislike he clearly developed for Romney during the primaries; the above quote makes me think McCain still has a bit of a way to go in that department.
Update: I now see, via Ambinder, that First Read interprets the joke as all in good fun and a sign that McCain is warming to Romney:
Bada bing. If McCain can start joking about someone, you know they've made it into his mental inner circle.
What can I say? McCain is a riddle wrapped in a mystery inside an enigma.