President-elect Donald Trump has won the presidential election fair and square — indeed, decisively. He will be the 47th president of the United States. As the nation readies itself for another four years of Mr. Trump, it’s understandable to fear the worst — but healthy to hope for the best.

We have no illusions about Mr. Trump, his promises of revenge and his plans to staff the government with political deconstructionists. He did not conceal who he really is during this campaign. He won anyway. Democracy requires accepting the results however much one wishes they had come out differently, and even when the victor himself has failed to do so in the past.

Those understandably worried about another Trump term need also to keep an open mind regarding the reasons it is occurring and how, in fact, Mr. Trump broadened his support, forging a diverse coalition. It won’t do to dismiss a majority of the country as biased, ignorant or otherwise basely motivated. Yes, prejudices against foreigners, people of color and other targets of Mr. Trump’s rhetoric surely play a part in his extraordinarily durable appeal, but they can’t explain it all; indeed, the condescension of elites is itself a factor against which his voters were protesting by supporting him.

Mr. Trump capitalized on deep frustration with inflation and irregular immigration, even though he proposes counterproductive “solutions” — 20% tariffs on all imports and mass deportations. And that frustration rang true with many Americans because they perceived that Democrats failed to address genuine concerns about rising prices and porous borders for too long. When 70% of the electorate thinks the country is on the wrong track, and the incumbent’s approval rating is about 40%, as President Joe Biden’s was on Election Day, that is a flashing red warning light for the people in the White House — but it didn’t seem to register with them.

Mr. Biden’s responsibility for this defeat runs deep. He ran against Mr. Trump in 2020 as a transitional figure, a bridge to the next generation, but he failed to recognize his own limitations. He was clearly slipping — physically and mentally — but insisted on running for a second term. Rather than raise difficult questions about this, Democrats and Mr. Trump’s critics acquiesced lest a succession struggle help Mr. Trump.

Mr. Biden stepped aside only after a disastrous June debate performance caused a Democratic revolt. By the time Vice President Kamala Harris emerged as the Democratic nominee a month later, many voters had grown comfortable with the idea of voting for Mr. Trump over Mr. Biden. Now back in the political wilderness, Democrats should reflect on what they did — and did not do — right the last time they faced a Trump administration.

One key error was to lurch leftward ideologically. Ms. Harris herself staked out several unpopular positions, including a ban on fracking and support for taxpayer-funded gender-affirmation surgeries for undocumented detainees. These hobbled her this fall, even as she renounced some previous views.

Mr. Trump will take office again on Jan. 20, 2025, as a lame duck, ineligible under the Constitution to seek a third term in 2028. Accordingly, he does not need to be beholden to the radical elements of the far right. That creates an opening, should he choose to take it, to negotiate unexpectedly bold deals.

There will be many times when Democrats should vigorously oppose him. Mr. Trump’s isolationist policy instincts will require checking, especially regarding Ukraine’s war of defense against Russia. His potential to radicalize federal agencies, particularly the Justice Department, is a distinct danger. So are his undemocratic intentions to curtail press freedoms and to assert greater federal control over the District of Columbia. Even so, Democrats should be willing to look for areas of potential agreement.

Shortly before the election, Mr. Trump mused aloud that he shouldn’t have given up power four years ago. That’s chilling, especially in light of the bombast that characterized his campaign. The memories of Jan. 6, 2021, will forever be a stain on him — and a warning to this country.