If you believe the conventional wisdom, the presidential election is virtually finished. Barack Obama will win. Perhaps in a walk. Game over.

I don’t say this as a preference one way or the other — I have reached the stage in my journalistic career when I disapprove of most politicians — but simply as a matter of fact and logic.

The conventional wisdom, as I read it, rests heavily on the following propositions.

The economy is improving and will continue to improve, depriving the Republicans (and particularly the front-runner, former Massachusetts Gov. Mitt Romney) of their most powerful issue. This week, the government reported that economic growth hit a 3 percent annual rate in the fourth quarter of 2011. Not great, but better than recent performance.

●Romney and former Pennsylvania Sen. Rick Santorum, now his closest rival, are — each in his own way — alienating crucial independent voters. Romney is typecast as a wealthy businessman out of touch with most Americans. A recent Pew poll asked respondents whether he “understands the needs of people like you.” Only 31 percent agreed; 60 percent didn’t. For his part, Santorum is regarded as an extreme social conservative bent on imposing his moral code on the nation.

●The leading Republican candidates can be counted on to commit regular gaffes — Romney’s offhand comment about his wife’s Cadillacs, Santorum’s reference to the president as a “snob” — that make them look disconnected and un-presidential. In the general election, Obama will run circles around either of them.

●Finally, the Republican House of Representatives will serve as a priceless foil for Obama. It’s hard to overstate the public’s low esteem for Congress, especially the House. The latest monthly Political Report from the American Enterprise Institute discloses the following: 76 percent of Americans think most members of Congress should be defeated (although about 90 percent usually win re-election); only 12 percent think congressional Republicans have “brought the right kind of change to the country” (Obama scores 35 percent on this question); only 21 percent approve of how congressional Republicans are “handling their job” (Democrats score 33 percent). Controversial Republican governors in some battleground states (Wisconsin, Ohio) compound Obama’s advantage.

All in all, the conventional wisdom seems compelling. As a card-carrying member of the mainstream media — a group that creates and sustains the conventional wisdom -- I’m inclined to accept it. And yet there’s one conspicuous gap in the-election-is-already-over story: the polls. While the Republicans have been destroying each other and embarrassing themselves, the polls for a general election should have shown a collapse in Republican support. They haven’t — at least so far.

Go to Real Clear Politics for the latest figures. The average of the polls it follows shows (for the period from Feb. 10 to Feb. 29) Obama beating Romney by 4.6 percentage points (49 percent to 44.4 percent). Obama’s margin of victory over Santorum is slightly larger (49.3 percent to 44.2 percent).

If these were the final outcomes, they would be near-landslides, but at this point in the race — when the Republicans are attacking each other and Obama is also attacking them — the differences are fairly modest and not unusual. Guesses about the Electoral College lead to the same conclusion. Obama is ahead, but the outcome isn’t certain. Real Clear Politics gives him 227 electoral votes against 181 for the Republican nominee, with 130 in doubt; 270 are needed to win.

So it’s a puzzle. Logic and most evidence suggest the election is over. But the polls seem to dissent. Could it be that the real story is that Obama’s not a shoo-in even when he should be?