It is Kamala Harris’s Democratic Party now. The United Center here has had its roof blown off before, but seldom as explosively as it did on Thursday night. When Harris accepted the Democratic convention’s nomination for president, the hall erupted the way it did when NBA legend Michael Jordan would commit some jaw-dropping violation of the law of gravity.

She and her running mate, Minnesota Gov. Tim Walz, will lead the party in a crusade that Harris called “a fight for America’s future.” The beginning of Harris’s speech was autobiographical and the end was political, but a good deal of the middle was prosecutorial: She laid out the case against ever allowing Donald Trump back into the White House.

The arena was perhaps at its loudest when she led the crowd in what has become a rallying cry: “We’re not going back!”

I have to remind myself that it has only been one month since President Joe Biden stepped aside - or was pushed, some might argue - and gave his support to Harris. Thirty-two days, to be precise. So much has changed so quickly in our politics that it hadn’t fully sunk in, at least for me, how truly historic Harris’s nomination would be. Not until Thursday night. It is quite possible that the next president of the United States will be a woman of color; a woman who is Black and South Asian; a woman who is the daughter of immigrants from Jamaica and India. A woman who graduated from a historically Black college, Howard University. A woman who belongs to Alpha Kappa Alpha, one of the “Divine Nine” historically Black sororities and fraternities. A woman who is part of an interracial marriage and the “Momala” in a blended family.

Harris is the embodiment of the nation’s diversity, complexity and multiculturalism. She is a mirror, reflecting not America’s future but its present. The election might hinge on whether Trump can make voters feel unnerved or frightened by what they see. Much of the evening was clearly aimed at independents and Trump-weary Republicans, offering reassurance and creating a permission structure allowing them to vote for a Democrat.

This moment is “a precious, fleeting opportunity to move past the bitterness, cynicism and divisive battles of the past,” Harris said. “I know there are people of various political views watching tonight. And I want you to know: I promise to be a president for all Americans.”

Earlier, in a moment that could have been cribbed from the script of a Republican convention, Rep. Ruben Gallego (Ariz.), a Marine Corps veteran who fought in Iraq, brought onto the stage all the Democratic members of Congress who have served in the military. It was a gaudy display of unapologetic, unalloyed, flag-waving patriotism.

Rarely mentioned, though, was an issue on which Democrats disagree: the war in Gaza. Opponents of Israel’s war policy were denied the chance to speak from the podium. They will not forget.

Democrats cannot rest on their laurels because they haven’t won anything yet. They produced a star-studded, four-night, multi-hour television infomercial that went off pretty much without a hitch. They painted Harris as the avatar of a bright, hopeful future. And they dismissed Trump, in House Minority Leader Hakeem Jeffries’s memorable analogy, as the rejected former boyfriend to whom the nation should say, “Bro, we broke up with you for a reason.”

Still, the race for the White House could go either way. Harris clearly has enjoyed momentum and the convention might give her a further bump in the national polls, but the decisive swing states are very much up for grabs. Democrats have reason to feel good about their chances of regaining control of the House; holding the Senate, though, will be tough no matter what happens at the top of the ballot.

Perhaps the most important goal the party accomplished in Chicago was to reclaim a powerful word: freedom. Nothing is more central to the nation’s idea of itself, and speaker after speaker framed Democratic Party policy positions in terms of freedom. “When we Democrats talk about freedom, we mean … freedom to make your own health-care decisions, your kids’ freedom to go to school without worrying about being shot,” Walz said on Wednesday.

Republicans, accustomed to having a monopoly on the “freedom” brand, have not yet come up with any kind of coherent response. They will, though. This fight is just beginning.

Eugene Robinson is a Washington Post columnist.