By the time the first presidential debate adjourns Wednesday night, we’ll probably know whether Mitt Romney’s candidacy is on the mend or circling the drain.

His maiden faceoff with President Obama is arguably his last best chance to halt his steady poll erosion and dispel the perception that he’s the most ineffectual candidate since Bob Dole in 1996. (You don’t remember a thing that Dole did or said? I rest my case.) But for Romney, the hour is already late.

One debate — actually there are three, but the first is most important — can’t wipe the slate clean. One debate can’t magically erase the image that has taken root, of a guy from the one percent who seems out of touch with the average Joe, a conviction-free candidate who has refused to fill in the details of his bare-bones budget, tax, and economic plans.

It’s tough to rewrite a campaign’s prevailing narrative in a mere 90 minutes. Romney has been running for the White House since 2006, and if the tiny percentage of undecided voters don’t know where he stands by now, they’re not likely to feel more enlightened after the closing statements. And Obama will take every opportunity to reinforce that narrative. An incumbent with a solid lead in the key swing states clearly has the much easier job.

I don’t mean to suggest that Obama will ace the Wednesday test with ease. Lest we forget, he’s not a great debater. He was inconsistent during the long ‘08 campaign; on occasion, he was also lordly and condescending (“You’re likable enough, Hillary”). And, of course, he hasn’t debated since. He’s out of practice, and on Wednesday he’ll be on a stage devoid of presidential trappings. It’s no coincidence that incumbents sometimes lose the first debate; it happened to George W. Bush in 2004.

But even though John Kerry was widely judged the winner that night, he failed to change the prevailing narrative of that campaign. The Bush team had already painted him as a charisma-challenged flip-flopper, and that doomed Kerry in November. Romney, at this point, is in similar straits. In Wednesday’s debate, Obama can play the flip-flop card by merely quoting Romney himself — the 2007 Romney, who extolled health-care reform and who insisted that his landmark Massachusetts law, which requires that all citizens buy coverage, would be great for America. (Actual quote: “Our program is based on a private model health insurance program and that model will work for the nation.”)

More important, there’s the charisma factor.

I could pack this column with paragraphs of wonky policy issues, but let’s not kid ourselves: Presidential debates are not really about the issues. They’re about how the candidates look, behave, act, and react while talking about the issues.

Voters at home ask themselves, “Which of these guys do I really want to see on my screen for the next four years?” Obviously, the voters who hate Obama want him off the screen, but the fact is, most Americans — even those who are disappointed in him — still like him. They have a comfort level with him. Whereas Romney has the Al Gore disease; in his 30-odd debates during the GOP primaries, he often seemed stiff and awkward, especially when forced to improvise. And when he’s on script, he can’t connect with the working stiff; in the apt words of New Yorker magazine contributor Nicholas Leeman, “He talks to voters businessman to businessman, on the assumption that everybody either runs a business or wants to start one.”