CHARLOTTE — This city threw a street fair on Monday for the visiting Democrats, and it was a jovial bash. Anyone walking through downtown felt the party mood. It was certainly political — the range of Obamagear on display would do any sports franchise proud — but it also transcended the convention. Charlotte seemed happy to have the Democrats here.

The contrast with the Tampa convention was conspicuous. The Republican affair felt so terribly businesslike. Tampa was not nearly as invested in the GOP as Charlotte is in the Democrats. I tested my perceptions with those of colleagues who had also been in Tampa, and to a person, they sensed the same thing: The Charlotte Democrats seemed to be having the better time, and the mood here was more seemed more ebullient.

 Some of this is inevitable and reflects less on the nature of Republicans than on the nature of cities. Cities are democratic. They are also diverse, and Democrats are the far more diverse party. It may be inevitable that cities will throw themselves into a Democratic conclave in a way that they will never embrace Republicans.

But this may also relate to something else: In both Tampa and Charlotte, the most important figure was Barack Obama. The Republicans’ zeal focused far less on an embrace of Mitt Romney than a steely determination to remove from office an incumbent president many of them genuinely despise. The single most important reason Republicans were for Romney was the fact that he is not Obama.

There is certainly the mirror image of that negative feeling here. In my conversations at various gatherings so far, I found Democrats aghast at how far to the right the Republican Party has moved and petrified of how the country would be governed if the GOP were to win power.

Yet Obama himself still generates real enthusiasm, if not the “the excitement of history and the expectations of a new era” that my old friend Adam Nagourney nicely described this morning in the New York Times.

  The “Yes We Can” slogan has been replaced (implicitly) by “Yes We Must.” The “We can change the world” attitude is on hold for now. The new idea is closer to: “We’ll see this through.”

And nothing better captured the Obama campaign’s dilemma than the difficulty its spokespeople had on the Sunday talk shows in answering the classic Reagan question: Are you better off now than you were four years ago?” It was remarkable lapse that a bunch of very smart operatives had not settled long ago on the clear and obvious answer: Of course the country is better off than when Obama took over an economy that was close to collapse. It’s still not as good as it needs to be, and Obama, unlike Romney, has the policies to get us the rest of the way.

Still, this is a party that knows its fate is tied to Obama’s, and most in the ranks have not given up on the idea that his presidency will be one of historic achievements — as long as he is given four more years to preserve and extend them.

In that sense, the relevant contrast is not between Charlotte and Tampa but between Charlotte 2012 and the 1980 Democratic convention in New York City, where Jimmy Carter was renominated in the face of reluctance and unhappiness among the forces still committed the late Sen. Edward M. Kennedy’s challenge. (It’s worth noting that an emotional high point of tonight’s convention opening will be a video tribute to the Ted Kennedy’s life and achievements.)

Carter had to lead a divided party against Ronald Reagan. Obama may generate some impatience among Democrats, but he leads a united party that shudders at the prospect of his defeat. This alone won’t get him reelected. But it’s one of the central reasons — even in economic times that need to be explained with care — that he’s still very much in the fight.