John McCain is set to endorse Mitt Romney today, and I’m sure there will be plenty of platitudes.

But the McCain endorsement comes with baggage, like this:

“Never get into a wrestling match with a pig,” Senator John McCain said in New Hampshire this month after reporters asked him about Mr. Romney. “You both get dirty, and the pig likes it.”

Mike Huckabee’s pugilistic campaign chairman, Ed Rollins, appeared to stop just short of threatening Mr. Romney with physical violence at one point. “What I have to do is make sure that my anger with a guy like Romney, whose teeth I want to knock out, doesn’t get in the way of my thought process,” Mr. Rollins said.

Campaign insiders and outside strategists point to several factors driving the ill will, most notably, Mr. Romney’s attacks on opponents in television commercials, the perception of him as an ideological panderer and resentment about his seemingly unlimited resources as others have struggled to raise cash.

And the ads McCain successfully ran against Romney in response to Romney’s attack ads were brutally effective, and could be used by Obama almost off the shelf:

All of that will be forgotten, or will it?

Update:  Hmmm…. Gingrich super PAC uses McCain ’08 Web ad ‘Two Mitts’ to slam Romney:

On Wednesday, a super PAC backing Gingrich welcomed McCain’s endorsement of former Massachusetts governor Mitt Romney (R) by seizing on a Web ad, “Two Mitts,” that the Arizona Republican had run against Romney during the 2008 GOP nominating battle.

The spot juxtaposes clips of Mitt Romney stating contrasting positions on issues including abortion rights and gun control throughout his political career.