Oops, he did it again.

Texas Gov. Rick Perry — he of the shaky (to put it charitably) Republican presidential debate performances — tried and failed Wednesday night, for the better part of a minute, to name the three federal agencies he would eliminate as president. Even by his own standard of gaffery, this was bad.

“The third agency of government I would — I would do away with,” he said. “Education, the . . . Commerce and, let’s see. I can’t. The third one, I can’t. Sorry. Oops.” Never a good sign when even the debate moderators are laughing at you, along with the audience.

Forgetting something on live television isn’t necessarily a death sentence. Arizona Gov. Jan Brewer (R) froze up during a debate in 2010 and went on to win easily. But what makes this episode so damaging for Perry is that it plays into preexisting doubts about whether he is ready for prime time. Not to mention that an energy plan has been one of the cornerstones of his proposed economic reforms.

To his credit, Perry owned up to his gaffe — “Yeah, I stepped in it, man,” he told reporters in the post-debate spin room — and tried to make light of it with an appearance on the “Late Show With David Letterman” on Thursday.

Laughter may be the best medicine, but even it can’t save a candidate already on political life support. And Perry and his people — deep down in places they don’t like to talk about at parties — seem to know it.

Rick Perry, for becoming a punch line rather than a presidential candidate, you had the worst week in Washington. Congrats, or something.

Have a candidate for the Worst Week in Washington? E-mail Chris Cillizza at chris.cillizza@wpost.com .

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