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 face-off 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 - 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 1 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 doesn't know where he stands by now, it's 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 that 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 Lemann, "He talks to voters businessman to businessman, on the assumption that everybody either runs a business or wants to start one."

There will be much policy talk in these debates about the economy, the deficit, Medicare, Obamacare, Libya, Israel, Iran, the whole nine yards. But viewers will likely look for character cues, those rare moments when a candidate inadvertently reveals something real about himself (or something that seems real, or something that confirms what people already think is real).

So it went in 1976, when President Gerald R. Ford inexplicably insisted that the Soviets did not dominate Poland (reinforcing the perception that he was a tad slow on the uptake); in 1988, when Michael S. Dukakis spoke in legalese after he was asked how he would respond if his wife were raped and murdered (reinforcing the perception that he was soulless and robotic); and in 1992, when President George H.W. Bush peeked at his watch in the midst of a debate in which he was taking citizen questions (reinforcing the perception that he was out of touch with people's pain).

Ah, yes, spontaneity. And this is where Romney really needs to be careful.

Off script, his character cues have hurt him - such as when he said that the $374,000 he earned in speaking fees over a recent 12-month span was "not very much," or when he said that America's "middle income" was between "$200,000 and $250,000" (the nation's median income is $50,000), or when he boasted that wife Ann has "a couple of Cadillacs." Granted, those were not debate remarks. But it was during a debate when he turned to Rick Perry, in the midst of a policy dispute, and said, "Ten thousand bucks? Ten thousand dollar bet?"

I'll go out on a limb here and suggest that the median-income lunch-pail lugger would be reluctant to place 20 percent of his annual pay on a sporting bet. If Romney says anything on Wednesday that's even remotely like what he said to Perry, he'll be dead politically Thursday. Rest assured, he has been warned.

But his biggest problem is that fat-cat fund-raising video, where, in private, he painted "47 percent" of the electorate as government-addicted moochers who pay no income taxes and who refuse to take responsibility for themselves. (The moochers include soldiers, seniors, young people, and the working poor.) Obama has launched a new ad that quotes from the video, and don't be surprised if he alludes to it in the debate, if only to make Romney play defense.

Obama, aided greatly by Romney's unforced errors, has managed to make this race a referendum on the challenger. The "47 percent" video has fed the prevailing narrative and buttressed Obama's poll rise. Indeed, Romney's hopes for a miracle comeback may be dashed if nearly half the American public watches the first debate and wonders:

"What difference does it make what he says to our face, when we already know what he says about us behind our backs?"