WASHINGTON — And so it was over. Just like that. The moving trucks behind the White House packed up 43 and unpacked 44. George W. Bush accompanied the man who had pilloried him up to the Capitol. Barack H. Obama was sworn in to office by the chief justice he had voted against confirming.

The transition happened with all the order we take for granted in our contentious democracy. Finally, a helicopter lifted the former president into the air and nearly 2 million people seemed to exhale as if witnessing the final fade-out in a long, long movie.

This swarm of people as diverse as the extended first family, as unique as each hat, as united by emotions as they were by the frigid air, began to inch out onto the streets of the city. Behind me an older, white Alabama woman said, again, “I never thought I’d live to see this day.” It was less a cliche than the mantra of the day.

Just two years ago, cover stories asked “Are We Ready for an African-American President?” The campaign posters had urged “Yes We Can.” Now the souvenirs were boasting “Yes We Did.”

“What the cynics fail to understand is that the ground has shifted beneath them,” said the new president in his inaugural address. You could feel this shift on the Mall, the same ground where slaves were once sold. You could feel Americans of all colors flush with surprised pride that we had measured up to our own dreams.

Walking down K Street, the boulevard of lobbyists turned into the avenue of hawkers, I stopped to get a T-shirt for my grandson. It showed Obama opening his neat shirt to reveal a Superman costume.

His speech, however, had been more sober than triumphant. Indeed, during the run-up to the inaugural, his inner circle had tried to tamp down such heroic expectations. As Spike Lee had said quietly: “He’s not the messiah.” We know that he can’t truly reboot the country — in our favorite computer image — cleansing it from all the viruses, the worms and glitches lodged in our national hard drive.

But the enthusiasm, the palpable sense of that much-overused word “hope,” seems to have arrived in direct proportion to our need. It’s as if this president is what — all? — we have going for us.

Obama did not need to do more than touch on the “sapping of confidence across our land; a nagging fear that America’s decline is inevitable, that the next generation must lower its sights.” What he tapped into as well is the willingness of these same Americans to “pick ourselves up, dust ourselves off” and, most astonishingly, invest in another leader.

Trust has been a bear market. After the collapse of faith in every sort of expert — after lenders financed houses for people who couldn’t afford them, bankers created systems they couldn’t even describe, and, finally, we hear, Bernie Madoff ripped off even his high school friends — there is a residue of resilience.

The latest polls tell us that a majority of Americans actually expect this president to achieve every one of 10 campaign promises from alternative energy to health insurance. Web sites and billboards are collecting individual hopes like pennies from heaven and the text-message on my iPhone relayed the “hopes” of one 6-year-old grandson who wants the new president to make peace and help the poor. That’s all.

The world did not stop for Barack Obama. Before lunch was over, he was leaning over Ted Kennedy, the lion of the Senate fallen ill. Before the Punahou band had passed the parade reviewing stand, the stock market had plummeted 332 points. Before we stop analyzing the “new era of responsibility,” he will be held responsible for everything from tainted peanut butter in crackers to enhanced nuclear fuel in Iran. Already, snarky blogsters and cablemeisters are betting how long the honeymoon will last.

And yet, in a city of people who had to be together on the Mall, something in the spirit chose to believe with the president that “our patchwork heritage is a strength, not a weakness.” Something chose to celebrate that “our time of standing pat … has surely passed.”

In 1787, when the Constitutional Convention was over, a woman asked Ben Franklin whether we had a republic or a monarchy. “A republic,” he answered, “if you can keep it.” On this astonishing week, America won another chance. If we can grab it.