As Mitt Romney slides in the polls, conventional wisdom holds that the first presidential debate on Wednesday is his last big chance to regain the momentum. Both sides are trying to lower expectations, with Team Romney noting that President Obama is a "universally acclaimed public speaker" and Obama aides openly worrying that the demands of being president are depriving their candidate of the time he needs to prepare. New Jersey Gov. Chris Christie, a key Romney backer, predicts the former Massachusetts governor will deliver a game-changing performance, although a majority of likely voters — 51 percent to 33 percent — expect Obama to come out on top. Here, four reasons why the debates probably won't change how Americans vote on election day, even if they produce some memorable gaffes or zingers:

1. The debates have been too watered down
Televised debates were once real slugfests, says Doug Mataconis at Outside the Beltway. The first one, in 1960, propelled a trailing but tanned and telegenic John F. Kennedy into the lead over a pale, sweating Richard Nixon. Ever since the Commission On Presidential Debates took over these showdowns in 1988, however, there has been "very little actual 'debating' between the candidates." Instead, all viewers get on any issue is "two to three minutes of platitudes followed by a response, [before] we move on to the next question." In rehearsals, handlers program their candidate to answer every conceivable question; all Obama and Romney have to do is fire off the right line at the appropriate moment. "This isn't Nixon-Kennedy 1960, and it certainly isn't Lincoln-Douglass 1858." It's a dog-and-pony show designed to make sure voters only hear scripted messages instead of a spontaneous exchange of ideas.

2. The debates arrive too late in the campaign
Scheduling the debates so close to election day dramatically reduces their impact, says Elise Hu at NPR. The first one takes place with just over a month left in the campaign, at which point early in-person voting has already started in several states. By then, almost all voters have made up their minds, and true fence-sitters are less likely to be glued to their sets than "the politically inclined who already favor one party or the other." Bottom line: The televised sparring is unlikely to sway the undecided voters Obama and Romney really want to reach. In the last 15 years, the candidate who was leading after the conventions went on to win the race, says Napp Nazworth at The Christian Post. That's why Obama launched a massive ad blitz at the end of the summer. After that, every day we get closer to the election, it gets a little harder to move the needle.

3. The debates are losing credibility by squeezing out third-partiers
There used to be some "wild and woolly days" in the debates back when the candidates "might be thrown curve balls by such unpredictable loose-cannon debate hosts... as the League of Women Voters," says J.D. Tucille at Reason. In the last two decades, though, the Republican and Democratic parties have won "a lot more control over the ritualistic meetings." Their drive for a "stage-managed, private-club quality" may have gone too far this year, though: The exclusion of third-party candidates like Gary Johnson of the Libertarian Party and Jill Stein of the Green Party has triggered a backlash. Three debate sponsors have pulled out so they won't be seen as endorsing the Republicans or Democrats, and now the whole process "is leaking credibility, not to mention financial viability."

4. Events in the real world easily overshadow debates
Perceptions matter, so any given debate could conceivably move the needle at least a little, says Scott Rasmussen at News Busters. "If Romney can get Obama to say something suggesting he values government workers more than those in the private sector," the GOP candidate might inch up in the polls, and if Obama can provoke Romney into saying something "that seems out of touch or mean-spirited," he might gain a little. Still, "events in the real world matter more than the debates." If anything is going to tip the scales on election day, it's far more likely to be a piece of blockbuster news that changes the way voters see the economy or the international front than a zinger delivered in a debate.

Read more political coverage at The Week's 2012 Election Center.