You know a campaign issue has traction when a mainstream magazine can capsulize it in a gimmick like Fortune's new "George W. Bush Suit-O-Meter," which purports, with a pen-and-ink silhouette topped by the head of the Texas governor, to measure the Republican front-runner's success in allaying fears that he's turning out to be an empty suit. It's a crude way of summarizing legitimate questions about whether Bush has the intellect to back up his spectacular political performance so far.

But the suddenly widespread concern about Bush's mastery of substance leaves untouched a question that may be equally important: Is Bush too peevish to be president? Bush's history suggests that he has struggled for much of his life with a kind of defensive anger--an anger more subtle, but perhaps more corrosive, than the temper tantrums of which his rival John McCain has been accused. Beneath the winning optimism of his politics he sometimes shows, even today, a curious air of resentment, which is all the more puzzling for its place in a life so touched by advantage.

He shows it in the way he discusses his years at Yale and Harvard Business School, when he looked around at classmates protesting war and racism, and found cause for indignation only in the fact that his peers dared to question their lives at the top of the heap. He has repeatedly fumed, in interviews, about how "arrogant" and "righteous" his fellow Yalies were, huffing, "These are the ones who felt so guilty that they had been given so many blessings in life--that they felt they should overcompensate by trying to give everyone else in life the same thing."

In his twenties and thirties, he was legendarily short-fused, especially when drinking. At 26 he challenged his father to a fight after the elder Bush reprimanded him for driving drunk with his 15-year-old brother in the car. And as The Post reported last year, he once berated and swore at journalist Al Hunt, in front of Hunt's small children, for the capital sin of predicting that then-Vice President Bush would lose the 1988 campaign for president.

What accounts for these flashes of petulance in such a lucky man? Most people explain the darker strains in his character by citing his high-pressure patrimony. It could indeed be a grinding burden to have your father presented, all your life, as both a man of unattainable grace and accomplishment and the model you must match in all things. But even more puzzling than where his resentment came from is the question of where (or more accurately, whether) it went. In Bush's account of his life, his rough edges were a function of youth and his fondness for drink; they were sanded smooth, he attests, by his 1986 decision to quit drinking, and by his increasing religious devotion. Yet these changes in his life preceded his performances as Sonny Corleone in his father's 1988 and 1992 campaigns.

Today, watching his breezy confidence on the campaign trail, it's often possible to credit what his friends say: that he has disciplined himself, and in making his own mark on the world has grown, or mellowed, out of his sullen streak. But then, suddenly, there it is--the flash of testiness; the grudging, pugilistic response, especially to questions about his intellect. He reads four newspapers a day, he told moderator Brit Hume in answer to a question during a recent debate. And then he couldn't resist adding, with the shadow of a sneer, "I'm not so sure I get a lot of knowledge out of them, but I read them every day."

This surly edge isn't by any means the dominant note in Bush's public persona. But neither is it something his fans can wish away. Especially disturbing was his interview last summer with Talk magazine, in which he ridiculed Karla Faye Tucker, a murderer who was executed in Texas in 1998. Writer Tucker Carlson reported that Bush snapped at him for asking about the many pleas for clemency that had flooded into the governor's office, and then mimicked the repentant prisoner's own pleas for mercy: "Please," Bush whimpers, his lips pursed in mock desperation, "don't kill me."

He actually seemed to bear the dead woman a grudge for the political headaches she had caused him.

Petty angers like this, strangely, may be more worrisome in a candidate than the booming temper of which McCain stands accused. At least those who give voice to their tantrums, LBJ-like, tend to reach tranquillity on the other side. But in a president, sins of small-mindedness are rarely small flaws. Our most resentful recent leaders, surely, have been Richard Nixon and Bill Clinton. Clinton's legacy will be forever tarred by the mulish self-pity and blame-laying with which he helped to extend and worsen the impeachment drama. Nixon was, and Clinton is, among the smartest presidents we've had--a distinction that did little to spare either from the ruinous weight of the chip on his shoulder.