WHY MUST HE BE SUCH AN ANGRY OLD MAN…. Most good stories have heroes, and when it comes to the story of repealing “Don’t Ask, Don’t Tell,” the list of heroes is wonderfully long.

And then there are the villains.

If John McCain gets any more hostile toward his Senate colleagues, they might consider having him go through the metal detector before he enters the Capitol.

Saturday’s debate on the repeal of the “don’t ask, don’t tell” policy was only half an hour old when the Arizona Republican burst onto the floor from the cloakroom, hiked up his pants and stalked over to his friend Joe Lieberman (I-Conn.) and Senate Majority Whip Dick Durbin (D-Ill.). Ignoring Sen. Jim Inhofe (R-Okla.), who had the floor, McCain hectored the men noisily for a few moments, waving his arms for emphasis.

When McCain finally stormed off, Durbin shook his head in exasperation and Lieberman smiled. A minute later, McCain returned — he had apparently remembered another element of his grievance — and resumed his harangue.

Watching McCain rail endlessly yesterday was a genuinely painful experience. In one sense, he was practically embracing the caricature of himself, lashing out as a bitter, cantankerous ass. I kept expected McCain to start shaking his fist at clouds and demanding that children stay off his lawn.

But that’s really not that unusual anymore, and it’s only part of a larger picture. McCain wasn’t just an angry old man yesterday; what we saw was darker and uglier. The Arizona senator on the floor yesterday, with a series of cringe-worthy tantrums, was hateful and filled with bile. McCain was even sarcastic at times, as if he almost relished the role.

This wasn’t about policy. By all appearances, this was personal.

When we look back at the apartheid-loving segregationists of the 1950s and 1960s, most decent people see racists and misguided monsters. Yesterday, it seemed as if McCain decided, perhaps deliberately, that he wanted to be that guy for the 21st century. Why? I obviously can’t read the conservative senator’s mind, but it seemed to have something to with (a) his intense disgust for President Obama and anything he wants; and (b) his revulsion towards gay people.

If you missed the display, you missed McCain arguing:

* The tripartisan majority supporting repeal are acting “in direct repudiation” to the wishes of the public (which, incidentally, strongly supports repeal).

* Apropos of nothing, McCain said he’s launched this crusade because, “You go up to Bethesda Naval Hospital, Marines are up there with no legs, none. You’ve got Marines at Walter Reed with no limbs.”

* At one point, McCain said, “I’m aware that this vote will probably pass today … and there will be high fives all over the liberal bastions of America. And we’ll see the talk shows tomorrow, a bunch of people talking about how great it is. Most of them never have served in the military or maybe not even known someone in the military.” (That will be news to the decorated war heroes who voted for repeal yesterday, including Jim Webb and Daniel Inouye.)

This isn’t another “Whatever happened to the old McCain?” piece, which we’ve all seen too many times in recent years. Rather, this is to suggest McCain has done more than make the transition from “maverick” to petulant right-winger. Yesterday, the man waving his arms on the Senate floor was a misanthropic hack who’s abandoned basic decency, and trashed any hopes he might have had about a respectable legacy.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.