Karl Rove was on Fox News on Monday evening, analyzing the latest polls and talking up the chances of his boy Mitt. “It’s a close race,” he insisted. “Candidates are rarely as bad as they think they are, or the conventional wisdom thinks they are, or rarely as good as the conventional wisdom thinks they are.” And Rove went on: “It’s going to come down to the last ballot, at the last moment, on the last evening of the election.”

Given that Rove helps to run the biggest Republican Super PAC, Romney will be pleased that he hasn’t given up on him. But is there a realistic possibility of the Mittster turning things around? History is against him. The most recent Real Clear Politics poll-of-polls shows him trailing Obama by 3.7 percentage points. As FiveThirtyEight’s Nate Silver noted in a useful statistical update, since 1936 the only candidates who went on to victory after being behind in the polls in late September were Harry Truman in 1948 and George W. Bush in 2000. From a Republican perspective, the state polls look even more depressing than the national ones. On Monday alone, nine more of them were released, and every single one showed a move toward Obama. Tuesday bought yet more grim news for the Republican candidate: a new Washington Post poll in which he is trailing by five points in Florida and eight points in Ohio.

At the British bookmakers, the odds of a Romney victory are now about 100/30, which means you have to bet thirty dollars to win a hundred. This implies that the probability of Romney winning is about twenty-three per cent. At Intrade, the online prediction site, the implied probability is just a bit higher: twenty-seven per cent. Expectations of an Obama victory could easily become self-fulfilling, with voters (and donors) shifting their support to the candidate they think more likely to win. Appearing with Rove, Joe Trippi, the Democratic strategist, pointed to evidence that some voters who had previously identified themselves as independent are now calling themselves Democrats. The Washington Post’s Ezra Klein raised the Romney “nightmare scenario” of his rich backers deserting him en masse.

Let me be clear: I remain confident enough that Obama will win that, if Rove or anybody else is willing to offer me even odds, or even one-to-two, I’d happily bet on it. But the future is inherently uncertain, and the possibility of a Romney comeback can’t be wholly discounted. Opinion polls and betting markets are best regarded as snapshots of the prevailing wisdom at given point in time. Even at this relatively late stage of the campaign, the picture can change. Since 1972, as Silver pointed out, the average change between the polls in late September and the result on Election Day is close to five per cent. That’s larger than Obama’s lead in the poll-of-polls. While Truman and George W. were the only victorious candidates to come from behind, others have come close. In 1968, Hubert Humphrey was trailing Richard Nixon by double digits, and he ended up losing by less than a point. Even Michael Dukakis, widely written off in September, rallied late to throw a scare into the Bush camp.

According to the betting markets, Romney still has about a one-in-four chance of winning, which suggests that the task facing him is equivalent to tossing a coin twice and getting two heads in a row. That’s not easy, obviously, but it isn’t entirely out of the question, and it’s an interesting exercise to think about how it could be achieved. Here, just for the sake of argument, is a Romney victory scenario.

The Labor Department revises down the number of jobs the economy has created in the past couple of years. It hasn’t been talked about much, but this Thursday the Labor Department will release its annual revisions to the job figures, covering the period from April, 2010, to December, 2011. Based upon comprehensive figures gathered at the state level, these revisions can be substantial. The 2010 revision removed three hundred and seventy-eight thousand jobs from the official tally; the 2011 revision added a hundred and sixty-two thousand. This year’s revision could go either way, but if it wipes out some of the jobs “created” during last year’s uptick in job creation, as reported in the monthly employment reports, it will give Romney some ammunition he badly needs. Romney does well in the first Presidential debate, which takes place in Denver next Wednesday. The one upside of Romney’s gaffe-plagued campaign is the low expectations it has created. As he showed during the G.O.P. primaries, he is a competent debater, with a willingness to beat up on his opponent where necessary. (Think Newt Gingrich in Jacksonville.) The subject of the first debate is domestic policy, which will give Romney a chance to go after Obama on his economic record and his lack of experience in the business world. Jim Lehrer, the moderator, will be keen to allay charges that he is too old or courtly to ask tough questions, but the onus will be on Romney to take control of the evening and challenge Obama head-to-head. Obama, doubtless, will be as articulate as usual, but for once he won’t be able to avoid talking about topics he generally avoids on the stump, such as the stimulus and the health-care-reform act. The September jobs figures are disappointing. They will come out on Friday, October 5th, just two days after the first debate. If Romney emerges from Denver on a high, a poor employment report could give him more momentum. For some reason—perhaps because the Democratic Convention overshadowed it—the August figure of just 96,000 jobs created didn’t have much political impact, but another weak number could prove more troublesome for Obama. Forecasting the monthly job figure is a mug’s game, but, for what it’s worth, the number of people filing jobless claims fell by just three thousand last week, suggesting that the labor market is still depressed. Paul Ryan outguns Joe Biden in the Veep debate, which is on Thursday, October 11th, and Romney holds his own in the second Presidential debate, which takes place in Hempstead, Long Island, on Tuesday, October 16th. With Ryan’s reputation as a good debater and Biden as a loose lips, the expectations game favors the Vice-President. But a gaffe on his part could still prove damaging. The second Presidential debate is a town-hall meeting moderated by CNN’s Candy Crowley. The format should favor Obama, but with real people asking the questions anything could happen. The national polls tighten up. Both campaigns have been saying they expect this to happen, but so far there hasn’t been any sign of it. A good performance by Romney and Ryan in the first two debates could be just what the Republicans need to rally their supporters and win over some independents. If the Republicans can narrow the gap to two or three points with a couple of weeks remaining before the election, they will be hopeful of pulling off a shocker. Amid more turmoil in the Middle East, Romney gets the best of Obama in the third and final Presidential debate, which takes place on Monday, October 22nd, in Boca Raton. The session will be devoted to national security and foreign policy, an area where the polls show Obama with a strong lead, but also one where the Republicans think he is vulnerable. Turmoil abroad, especially when it involves the deaths of Americans, is always damaging to incumbents. The week the American Ambassador to Libya was killed, Obama’s poll rating dropped even though Romney’s grandstanding response was widely criticized. Some key swing states move towards Romney. With the national polls tightening up, he moves comfortably ahead in Florida and North Carolina, and in Colorado, Iowa, Nevada, New Hampshire, Virginia, and Wisconsin he moves within striking distance. Ohio remains firmly in the Obama camp, but even without it there are eleven permutations that could see Romney to two hundred and seventy votes in the electoral college. (Thanks to Karl Rove for doing the combinatorial math.) On November 6th, the late-breakers swing in Romney’s favor, and he virtually ties Obama in the popular vote. With most of the swing states, but not Ohio, breaking his way, it all comes down to Virginia, where the exit polls show the race a lot tighter than expected. Finally, close to dawn on November 7th, it emerges that Romney has won by a few hundred votes.

O.K. It’s not likely to happen, and if it does many of you will move to Canada, or threaten to. But it’s something to think about. After all, who doesn’t enjoy a good disaster movie?

_See our full coverage of the campaign season at The Political Scene.

Photograph by Mandel Ngan/AFP/Getty.