In the 2008 presidential debate dedicated to foreign policy, Sen. John McCain tried to sound magisterial when he kept repeating the line “Sen. Obama doesn’t understand.”

Instead — and this is astonishingly easy for McCain — he sounded like a jerk.

Now comes Mitt Romney — whose magisterium, we’re told endlessly, is the economy — with the declaration that President Obama “just doesn’t have a clue.”

He sounds just as jerky as McCain did.

Now, somewhere in the recesses of the place he calls “Integrity,” Romney has no doubt he can bring his private-sector expertise to bear on the U.S. economy. But Romney did not become the presumptive GOP nominee because of his mastery of policy. If anything, Romney’s reputation as a technocrat —- on issues like, say, achieving near-universal health coverage for residents of Massachusetts -— earned him a heap of skepticism during the primary.

And so Romney has had to dumb himself down; or, alternatively, speak only in the breeziest of generalities about his business experience. As Jonathan Chait says of Romney’s interview with Time’s Mark Halperin: “Romney is just repeating his premise over and over again. He doesn’t say why his experience as a rich business guy better enables him to craft pro-growth policies.”

This is a function of Romney feeling forced to embrace the right’s negative vision of macroeconomics: government itself can’t create wealth; it can only create an environment in which wealth-creators (like private-equity companies!) create wealth.

Romney naturally doesn’t want to get into the weeds of how he created wealth when both the base of the Republican party and its elites want him to promise, fundamentally, to stay out of the way.

I get it. That’s the game.

But it beggars belief to affect this posture and, at the same time, insist that your opponent “doesn’t have a clue.”

What’s hard to “understand” about the supply-side agenda? Taxes: lower rates and simplify the code. Regulations: eliminate as many as possible. Spending: cut it, and then cut it some more.

Is President Obama too inexperienced or just plain thickheaded to comprehend this agenda?

Or does he philosophically disagree with it?

I’m not in a position to know exactly what Romney believes, but I do know this: if it’s in his interest to become more “likeable,” he should avoid sounding like John McCain.