Rick Perry should have backed off. Instead, he doubled down, and in a way that was doubly illuminating -- about Perry himself and the degraded state of modern politics.

The issue, amazingly enough, is President Obama's birthplace -- months after the release of his long-form birth certificate should have laid the matter to rest. In an interview with Parade magazine, the Texas governor declared Obama's place of birth a "distractive" issue even as he happily latched on to the opportunity to distract.

"Well, I don't have a definitive answer [about whether Obama was born in the United States], because he's never seen my birth certificate," Perry said. It was classic Perry: a trademark combination of logical incoherence and smarmy cheap shot.

A smarter candidate would have stopped there. Perry, in an interview with CNBC's John Harwood, kept going, despite Harwood's repeated invitations to walk back his silliness.

"Look, I haven't seen his," Perry said. "I haven't seen his grades. My grades ended up on the front page of the newspaper, so let's, you know, if we're going to show stuff, let's show stuff."

Is this a presidential campaign or a middle-school playground? I'll show you mine if you show me yours? By the way, if I had Perry's grades, I wouldn't be mentioning them. Certainly not if I were running against a former president of the Harvard Law Review.

But then Perry, as is his style, let on what this was really about. "But look, that's all a distraction. I mean, I get it. I'm really not worried about the president's birth certificate. It's fun to poke at him a little bit and say, 'Hey, how about let's see your grades and your birth certificate.' "

The matter of the president's birthplace, Perry added, is "a good issue to keep alive."

You might think this was the candidate cannily trying to have it both ways: a nod to the birther crazies with a simultaneous wink at those who know this is a ridiculous distraction. Except that Perry managed to step on his real message of the day: his unaffordable and unfair proposal to "simplify" the tax code -- by grafting a flat-tax alternative onto the existing system.

Now we have Perry, who has a decent if fading shot at the Republican presidential nomination, openly practicing politics as poke-fest. The point isn't to debate whose solutions are best for America -- it's to get under the other guy's skin.

Thus Perry needling Mitt Romney on immigration. "You hired illegals in your home and you knew about it for a year. And the idea that you stand here before us and talk about that you're strong on immigration is on its face the height of hypocrisy."

As it happens, Perry is righter -- that is, more correct -- than Romney on immigration, at least when it comes to the question of the DREAM Act and the ability of the children of illegal immigrants to obtain in-state tuition rates.

But Perry's jab at Romney was below the belt. The former Massachusetts governor employed a landscaping firm that, the Boston Globe discovered, had hired illegal immigrants. Romney told it to stop. When it turned out it hadn't, he fired the firm.

The matter of Obama's birth certificate should be a closed case. It is astonishing that a sitting governor, no less a serious candidate for president, would stoop to playing this game.

The country is facing serious problems. This will be a fateful election. Voters deserve better than scare tactics and drivel.