This is an old saw that's been going around for almost four years now. And I cannot tell you how many GOP operatives I've heard it from.
The idea is that John McCain either could have won or had a much better shot at it if he'd really released the hounds on then-candidate Obama. The idea being that McCain was just too honorable a guy or perhaps too much of a fuddy duddy to really do what had to be done to win. If only the campaign or the RNC had prepped a few dozen commercials featuring Obama in a foot-wide-brim pink fur hat, maxing around with Jeremiah Wright and Weather Underground terrorists about to send his race army of ill-tempered rappers to shake down a few good white folk, the thinking goes, he would have just come apart at the seams.
That's most of what is behind the continued, and, in some ways, really passionately believed mantra on the right that Obama was never really 'vetted.' If we'd only said Kenya a few more times we could have done this thing!
But here's the key: McCain -- or more likely his senior advisors -- weren't doing Obama any favors. There's a calculus in all of these decisions. Yes, going full race, terrorist pal Crazy on Obama probably would have gotten some voters more suspicious of Obama or more ginned up to vote against him. But it also would have repelled a lot of loosely affiliated voters in the middle. The McCain camp realized that. At least the more seasoned folks. And the Romney team gets it just as much.
The whole thing amounts to a fantasy of the right-wing id, not altogether unlike some of the hits on President Bush that the general public just didn't take to. Everybody heard about Jeremiah Wright. Everybody found out the president is black. It didn't turn the public against Obama when he was a relative unknown back in 2008. And it's far less likely to today.