It happens to all of us: your train of thought suddenly evaporates, a name or a word just won’t bubble up to consciousness when you need it. A singer forgot the words to “The Star Spangled Banner” before a ball game last summer. Most of us just laugh it off and dismiss it as a “senior moment.”

But presidential candidates are held to different standards. Under intense scrutiny, their every word is weighed, their every reaction judged, their every gaffe endlessly discussed both in the media and in the court of public opinion. That’s why I always find it so irritating when someone calls a president stupid, as liberals invariably do when the president is a Republican (except Nixon: he wasn’t stupid, he was evil). No one remotely stupid could possibly survive the endless gauntlet of a presidential campaign, with thousands of reporters, photographers, and cameramen praying for them to commit a major gaffe, and laying traps to help them do so (such as asking who the prime minister of some obscure country is).

Sometimes a candidate or a president can turn the mistake to their advantage. George W. Bush did exactly that with his occasional malapropisms. So did Fiorello H. LaGuardia with his famous confession that “When I make a mistake, it’s a beaut!” But sometimes a gaffe that really doesn’t seem all that important–and Perry’s memory lapse was hardly more than a slip of the tongue after all–can be almost instantly fatal, at least politically.

As he watched Perry squirm last night, I wonder if Mitt Romney was thinking of his father, George, who was a major contender for the 1968 Republican nomination until he admitted to having been “brainwashed” about Vietnam. In the blink of an eye, he was political toast. (Helping him over the cliff, of course, was Senator Eugene McCarthy, running for the Democratic nomination and known for his wit, who said he didn’t see why Romney needed to be brainwashed, “a light rinse would have done it.”)

The next few days will reveal whether this is a one-day story among the chattering classes or the effective end of the Perry campaign. That campaign has been going badly, so perhaps this relatively minor incident will be the straw that breaks the camel’s back. Or perhaps it will be forgotten.