By any objective measure, Mitt Romney has flip-flopped more often, on more issues, than any American politician in a generation. It’s quite embarrassing — the guy reinvents himself periodically, shedding one version with one set of positions, and becoming an entirely new person with new positions. Mitt Romney is like a box of chocolates — you never know what you’re going to get.

So, when the subject of consistency came up in last night’s debate, it was a rare opportunity for Rick Perry to hammer Romney on one of his biggest vulnerabilities. But the Texas governor, who’s just genuinely awful in these debates, somehow managed to screw it up.

PERRY: I think Americans just don’t know sometimes which Mitt Romney they’re dealing with. Is it the Mitt Romney that was on the side of against the Second Amendment before he was for the Second Amendment? Was it — was before he was before the social programs, from the standpoint of he was for standing up for Roe v. Wade before he was against Roe v. Wade? He was for Race to the Top, he’s for Obamacare, and now he’s against it. I mean, we’ll wait until tomorrow and — and — and see which Mitt Romney we’re really talking to tonight.

WALLACE: Governor Romney?

ROMNEY: I’ll use the same term again: Nice try. Governor, I’m — I wrote a book two years ago, and I laid out in that book what my views are on a wide range of issues. I’m a conservative businessman. I haven’t spent my life in politics. I spent my life in business. I know how jobs come, how jobs go. My positions are laid out in that book. I stand by them. Governor Perry, you wrote a book six months ago. You’re already retreating from the positions that were in that book.

PERRY: Not an — not an — not an inch, sir.

ROMNEY: Yeah, well, in that book, it says that Social Security was forced upon the American people. It says that, by any measure, Social Security is a failure. Not to 75 million people. And you also said that – – that Social Security should be returned to the states. Now, those are the positions in your book. And simply, in my view, I stand by my positions. I’m proud of them.

Let me get this straight. The issue of flip-flops came up, and Perry let Romney get the better of him? Seriously? The most shamelessly inconsistent politician in recent memory simply ran circles around Perry on the subject of policy reversals?

Let me make this really easy for Perry. It’s a list that’s so obvious, even he should be able to memorize it: Romney is a former one-term governor who supported abortion rights, gay rights, gun control, immigration reform, and combating climate change, who distanced himself from Reagan, attended Planned Parenthood fundraisers, and helped create the blueprint for the Affordable Care Act. Romney was for the bank bailout before he was against it; he was against the auto industry rescue before he was for it; and he was for the stimulus before he was against it. Republican primary voters haven’t heard much about any of this, but it’s likely they’d find this history interesting.

Hearing Romney proclaim, “I stand by my positions,” may be the single most amusing thing said by a Republican this year.

How did Perry manage to flub this opportunity?

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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.