GENEVA — Standing under the wing of Air Force One in Geneva on Wednesday — after a weeklong trip abroad in which he repeatedly extolled the virtues of democracy over autocracy — President Joe Biden seemed briefly to knock his own product.

“I never anticipated — notwithstanding, no matter how persuasive President [Donald] Trump was — that we’d have people attacking and breaking down the doors of the United States Capitol,” Biden told reporters, referring to the Jan. 6 insurrection in the former president’s name. “I didn’t think that would happen; I didn’t think I’d see that in my lifetime.”

But then, like any good pitchman, Biden quickly regained his footing. He said the deadly mob attack had simply reaffirmed what he’d long been taught, by everyone from his political science professors to his former Senate colleagues: “Every generation has to reestablish the basis of its fight for democracy. I mean, for real, literally, have to do it.”

As Biden hopscotched across Europe last week on his first trip abroad, his most prominent message, repeated everywhere, was the need for democracy to prevail over autocracy in what he cast as the existential challenge of the 21st century. America, he promised, was back at the helm of that struggle.

But the fight for democracy, or a version of it, is unfolding not just in Europe but also in the United States, and Biden’s message is complicated by the turmoil in the country he leads — the Jan. 6 attack, Trump’s baseless claim that the 2020 election was stolen, the push to restrict voting, the ongoing “audits” of elections whose results have long been settled.

In fighting for democratic values abroad, Biden risks seeming as though he is looking past the threats in his own country.

“Anytime you have a really divided country, it’s going to make the president look weaker,” said Michael Kazin, a Georgetown University historian. What is especially striking now, he added, is how many Americans question Biden’s victory and say they are open to political violence: “A disputed election is one thing. It’s another thing to have a large number of people in the losing party say that they don’t accept the results.”

Biden visibly wrestled with this challenge at times during his weeklong trip to Cornwall, Brussels and Geneva. At NATO headquarters in Brussels, he paused and let out a small sigh before answering a question about how the assault on the Capitol, and America’s polarized politics in general, might undercut his credibility with allies who know that Trump or a Trump-like figure could be back in power in Washington in a matter of years.

He essentially argued that Trump was an aberration. “I’m not making any promises to anyone that I don’t believe are overwhelmingly likely to be kept,” Biden said. European leaders, he added, “know our recent history — know, generically, the character of the American people” and believe, as he does, that “the American people are not going to sustain that kind of behavior.”

The dilemma is unlikely to fade anytime soon. Biden’s next foreign trip could come this fall, when the Group of 20 meets in Rome and a climate summit is held in Glasgow.

At the same time, Trump has signaled that he will ramp up his activities, holding rallies and endorsing candidates as he continues to promote the falsehood that the election was stolen, with many Republicans vocally agreeing.

And Biden also faces doubts from more liberal quarters.

Rep. Pramila Jayapal, D-Wash., the chairwoman of the Congressional Progressive Caucus, said democracy is in serious peril in the United States. Nevertheless, she said, that shouldn’t stop Biden from promoting democracy over autocracy on a global scale.

“There’s no question we have a lot of work to do to protect our democracy here, and I think we saw on Jan. 6 how close we came to losing it,” Jayapal said. “But I don’t think that undermines our ability to make that argument around the world. I actually think in some ways it strengthens our argument to say, ‘We are dealing with these same factors in the United States.’ ”