The inauguration of every new president is greeted with declarations of “a new beginning” and attended by enthusiasm, especially among the president’s partisans.

But President Barack Obama’s inauguration elicited a special outpouring — in the size of the crowds, the extent of cooperation between the outgoing and incoming administrations and a widespread atmosphere of good feeling.

Some of this uniqueness stems, of course, from the fact that Obama is America’s first African-American president, closing the nation’s ugliest historical wound.

And much of it, too, stems from the perilous condition of the nation’s economy, which lends an aura of “we’re all in this together” — because, among the wealthy as well as the needy, there is a shared sense of apprehension.

The special mood of this or any new beginning can’t be maintained indefinitely. One foundation executive said the lead-up to Jan. 20 reminded her of a weekend-long wedding party. Inevitably, the guests go home and the couple returns from its honeymoon to face the problems of real life.

It’s encouraging that, for the most part, Republicans and Democrats are going out of their way to be accommodating to one another, at least rhetorically.

For instance, when the Senate voted Jan. 15 on releasing the second half of the $700 billion bank rescue, Minority Leader Mitch McConnell (R-Ky.) expressed appreciation for the Obama transition’s cooperative attitude five times in a 10-paragraph floor speech.

On the other hand, McConnell and all but six other Republicans voted “no” on the extension, which Obama declared was necessary to save the financial system. Cooperation in dealing with the economic crisis has to begin to be substantive as well as procedural.

In his inaugural address, Obama set down a marker for the way politics needs to be conducted in the future. “On this day, we come to proclaim an end to the petty grievances and false promises, the recriminations and worn-out dogmas, that for far too long have strangled our politics.

“We remain a young nation, but in the words of scripture, the time has come to set aside childish things.” For at least 15 years, Congress has been the headquarters of “childish things” — a cauldron of partisan grievances and recriminations.

It is long past time for a fresh beginning. Both Obama and Sen. John McCain (R-Ariz.) called for it during the presidential campaign. It ought to happen now. It needs to happen in the House, particularly, with fair treatment of the minority by the majority.

Obama needs to follow through on his promises, too. He’s establishing himself as a pragmatist, not an ideologue, so it behooves him to at least consider new evidence from the Congressional Budget Office that his chosen remedy for the recession — massive infrastructure spending — might not have any economic effect until late next year.

That’s what many Republicans have been warning, and the point deserves his sincere attention.

As he said, this new beginning occurs “amidst gathering clouds and raging storms.” Republicans and Democrats are all in this together. They disagree philosophically, but the current crisis demands that they cooperate with each other, not thwart each other. That is, “set aside childish things” and act like grown-ups.