Every presidential campaign adds a little something to the store of conventional wisdom. For instance, 1960, 1988: Silly photo-ops and sweaty upper-lips can compromise a candidate’s image. 1992: Never make a pledge unless you’re sure you won’t break it. 1988, 1996, 2008: Republicans almost nominate the guy because it’s His Turn. 2000: If your party was in power during good times, you should emphasize that fact. 2004: Don’t let yourself be Swift Boated.

Before it has even begun in earnest, the 2012 campaign already has added this: Don’t believe the hype about bitter primary fights. I say this as a red-handed guilty party.

Romney has well and truly put the primary fight behind him. His favorability ratings have been climbing healthily — up 20 points since March, according to Washington Post/ABC News polling — and Republican voters are steadily growing more enthusiastic about his candidacy.

Philip Rucker of the Post has some good anecdotal reporting on how Romney is doing on the campaign trail lately:

Mitt Romney is still awkward sometimes, a bit robotic and stilted at the lectern. But a turnabout seems to be happening: Voters say they are seeing him through a new prism. …

Instead of polite clapping, Romney’s campaign speech riffs are cheered with hoots and whistles and chants of “Rom-ney! Rom-ney!” As he builds to the crescendo in his remarks — saying it’s time to take the torch and hold it up high so the United States can again become “that shining city on a hill” — his words are drowned out with bursts of applause.

Rucker notes that one of the factors boosting Romney’s confidence is that he’s increasingly seen as having a legitimate shot of unseating President Obama. The more Romney seems like a winner, the more he’s able to act like one.

All of this suggests that his trouble in the South, his embarrassing losses to the likes of Newt Gingrich and Rick Santorum, the air of skepticism that conservatives once greeted him with — it may as well have never happened.