Today may be the most important single day of the campaign. Obama won the debate. Everyone this side of Charles Krauthammer agrees that Romney was general and platitudinous and not that engaged. That makes two out of three. You might think that would mean momentum. And yet the conventional wisdom is congealing right now—it is hardening this morning, minute by minute—that Romney is going to win the election.

From Playbook, which distills the c.w.: President Obama won last night’s foreign-policy debate on substance, in snap polls and with the pundits, but Mitt Romney did well enough that for the first time in six years, Romney folks emailed, “We’re going to win.”

In reality, Obama is the favorite. The state maps still make him so. Nate Silver, the only person who takes every single poll into account (plus loads of other indicators), still has him so. This emerging c.w. is built more on spin and smell, which the media are starting to buy. One piece that Mike Allen bought this morning in that Playbook item: A Romney aide told him New Hampshire leans their way.

Ridiculous. Even RCP has Obama +3 in New Hampshire. A poll yesterday had him up nine. He’s never trailed there. It’s been a fight, true, but he is clearly on course to win it. But the Romney aide just threw it out there. Not blaming him or her—it’s the kind of thing you throw out when you want to start giving an impression of inevitability. But that is what the Romney team is trying now to do. (It’s up to journalism, of course, to say when something doesn’t seem true.)

And so, after their side’s third consecutive debate loss, conservatives are the ones feeling confident. They are creating a reality. They’re talking up Romney’s supposedly unstoppable momentum now that he’s survived the debates without making one of those Gerry Ford-style goofs (that’s the bar now for the presidency?). They’re tweeting things about Silver, sharpening their knives, contemplating his November 7 takedown. They’re not quite measuring the drapes, but they’re getting their rulers out of storage.

Factually, this isn’t remotely justified. At worst from Obama’s perspective, the thing is tied. As far as we know, looking at all the averages, on a state-by-state basis he’s ahead. If you assume seven or eight states in play and go through all the permutations, Obama often wins by taking just two or three of them. Yes, a lot hinges on Ohio. But he can win even without it (he needs a strong inside straight, but it’s possible). Romney absolutely cannot.

Conservatives know all this. But they’re constructing an opposite reality. This is at the heart of everything going on right now, I think. It’s what they can do that liberals can’t really do. They've always done it. “Romney is going to win” in 2012 isn’t so different from “We’ll be hailed as liberators” in 2003. They say something and try to make it so, and the media go for it time and time again.

This is what’s maddening to liberals about what Romney has done since the first debate. He’s constructed a new reality about himself and he’s gotten away with it, mostly. Specifically, it’s that he’s flip-flopped on all these things without the remotest hint of acknowledgement that the old positions even existed. Last night’s Afghanistan pirouette was stunning.

We’re used to a politician who says, “You know, I once thought…” or something like that. Then our minds can kind of buy the idea that he’s flip-flopping. Most pols do this. It used to be thought by political consultants that pols had to do that part of it. But not Romney and his team. No acknowledgement, not an inch. A complete lie. And a real f-you, by the way, to voters who’d like to know why he changed his mind, except why bother, really, since there’s no substance there. He changed his mind to win, period.

So today is the most crucial day of the campaign. Republicans are going to be filling journalists’ heads with the inevitability “reality”: a few poll results, a few morsels from the trail, and so on. A lot of the media will keep writing it that way, too.

What should Obama do? Well, Republicans want to make Democrats fearful and jittery and reactive—appear to be accepting the Republican premise. So basically, anything but that. These next two or three days will be crucial, and if the Democrats do seem fearful and reactive, they’ll help the new c.w. congeal and maybe help seal a fate that the facts don’t yet come close to foreordaining.