WASHINGTON -- Wednesday's presidential debate promises sharp contrasts. One candidate wants to repeal Obamacare, one candidate invented it. One opposed the auto industry bailout, one takes credit for it. One doubts the scientific consensus about climate change, one believes in it. One wants to "voucherize" Medicare, one wants to save it. One dismisses nearly half of Americans as a bunch of moochers, and one claims to champion the struggling middle class.
It promises to be an epic clash: Mitt Romney vs. Mitt Romney. Oh, and President Obama will be there, too.
In theory, the first general election debate is a trailing candidate's best opportunity to hit the reset button. New Jersey Republican Gov. Chris Christie, doing surrogate's duty on the Sunday morning shows, acknowledged that Romney has had a "tough couple of weeks" but promised the debate would change just about everything.
"This whole race is going to be turned upside-down come Thursday morning," he said on "Face the Nation."
In practice, debates are rarely decisive. Only in a few presidential elections have they demonstrably moved the needle. Perhaps this is one of those years, perhaps not. It seems to me that Romney's prospects Wednesday night will depend heavily on his ability to explain why he has taken so many different positions on so many issues.
He was "effectively pro-choice" before he was staunchly anti-abortion. He supported stricter gun control before he opposed it. He promises to cut everyone's taxes while also reducing the deficit, but won't explain how.
Romney gives the impression of being willing to say anything he believes voters want to hear. That's why the conservative Republican Party base is so vigilant, always on the lookout for signs that Romney is wavering on the hard-line positions he took during the primaries. Softening his views on immigration, for example, might help shrink Obama's overwhelming advantage among Latino voters. But the base won't allow it.
I believe Romney's history of ideological flexibility explains why his "47 percent" remarks were so damaging. It's not that his phrasing was inelegant, as the candidate and his surrogates maintain. It's that Romney was speaking behind closed doors, among like-minded friends, and finally we could glimpse what he really believes. We could see what's at his core -- and it wasn't a pretty sight.
Of course, Romney promptly denied that the smug and callous man in that grainy video -- the one who lamented he would "never convince" nearly half of his fellow Americans to "take personal responsibility and care for their lives" -- was the real Romney.
At this point, it's unclear to me that a "real" Romney exists. If one does, however, he'd better show up Wednesday night. If there's one thing we know about presidential debates, it's that voters can often look right through the persona and see the person.
In 2000, Al Gore's decision to make a show of walking up to George W. Bush during their debate and invading his personal space was correctly perceived as an awkward stunt. And when Gore sighed condescendingly while Bush was trying to talk, voters saw a side of Gore's personality they didn't like.
If Romney plans some kind of scripted "zinger" that somehow is designed to turn the whole election around -- a variation on Ronald Reagan's immortal "There you go again" -- viewers are likely to see through the artifice. He's not Reagan.
The same holds true for Obama, of course. But we know who Obama is and what he believes. Some people like him, some don't, but the nation has seen him in action for nearly four years. His job Wednesday night is clear: Defend his record and outline his plans for the next four years.
Romney's task is more difficult. For the umpteenth time, he has to introduce himself to the American people. He has to erase the impressions left by all the Mitt Romneys we met earlier -- the clueless rich guy, the heartless private-equity baron who likes "being able to fire people," the moderate who became a hard-line conservative and then became a little bit moderate again, kind of. And he has to reveal a coherent person, one whom voters can imagine as a leader.
The question is whether such a coherent person exists. In the business world, where Romney had great success, winning means saying whatever you need to close the deal. A presidential campaign, though, is different. At some point you have to say what you really believe.
Eugene Robinson's email address is email@example.com.Copyright 2012 Washington Post Writers Group