As noted below, Mitt Romney is having a great May, and John McCain just made it better, responding to Romney's opposition to the McCain jam down of the draft immigration bill with a personal attack on Romney, just as the Arizona senator did in last week's debate when Romney blasted the McCain-Feingold law:

Well, today, on a conference call with bloggers, Mr. McCain fired back at the former Massachusetts governor, who has (of course) held varying positions on immigration over the years.

"Maybe I should wait a couple weeks and see if it changes," Mr. McCain said of Mr. Romney's position on immigration this week. "Maybe he can get out his small varmint gun and drive those Guatemalans off his yard."

A McCain meltdown was widely expected at some point in the long campaign, but few people expected it so soon. 

The rejection of John McCain by the base of the Republican Party was predicted and explained in A Mormon In The White House.  Now the key question is whether Senator McCain will stay in the party and support its nominee, a question which hasn't been asked of him (or Tom Tancredo)and which should be, again and again until it gets a straight answer.

UPDATE: The Romney campaign responds:

“Governor Romney has been very clear that he opposes this immigration agreement, which clearly falls short of the American public’s expectations. It seems that certain candidates who brokered this flawed plan are having a very difficult time grappling with or coming to terms with the political fallout that has ensued in a substantive manner.”

-Kevin Madden, spokesman for Governor Romney