On the 20th anniversary of the terrorist attacks that changed his presidency, former president George W. Bush on Saturday warned there is growing evidence that domestic terrorism could pose as much of a threat to the United States as terrorism originating from abroad, and he urged Americans to confront “violence that gathers within.”

Without naming it, Bush seemed to condemn the Jan. 6 insurrection at the U.S. Capitol, when a pro-Trump mob overran the complex in a violent siege that resulted in the deaths of five people. Bush compared those “violent extremists at home” to the terrorists who had hijacked planes on Sept. 11, 2001, and crashed them in New York City, Arlington, and Shanksville, Pa., killing nearly 3,000 people.

“There is little cultural overlap between violent extremists abroad and violent extremists at home,” Bush said in a speech at the Flight 93 National Memorial in Shanksville. “But in their disdain for pluralism, in their disregard for human life, in their determination to defile national symbols — they are children of the same foul spirit, and it is our continuing duty to confront them.”

Bush, a Republican who was president when the 9/11 attacks happened, continually invoked “the nation I know” in his remarks Saturday, an echo of his previous rejection of the rhetoric of former president Donald Trump. Bush spoke of the difficulty of describing “the mix of feelings” everyone experienced on that clear September day 20 years ago.

“There was horror at the scale of destruction and awe at the bravery and kindness that rose to meet it,” Bush said. “There was shock at the audacity — audacity of evil — and gratitude for the heroism and decency that opposed it. In the sacrifice of the first responders, in the mutual aid of strangers, in the solidarity of grief and grace, the actions of an enemy revealed the spirit of a people. And we were proud of our wounded nation.”

As President Biden and Vice President Harris also did in remarks for the 20th anniversary of the attacks, Bush called on the nation to once again hold fast to its best qualities and shared strengths, to come together as many Americans felt the country had in the days after 9/11. Left unspoken — but alluded to plenty of times Saturday — was that the nation felt as divided as ever, and that Trump was continuing to stoke those divisions.

Here are key moments from ceremonies in New York, Arlington, Va., and Shanksville, Pa., to mark the 20th anniversary of the Sept. 11, 2001, attacks. (Joy Yi/The Washington Post)

“In the weeks and months following the 9/11 attacks, I was proud to lead an amazing, resilient, united people,” Bush said. “When it comes to the unity of America, those days seem distant from our own. Malign force seems at work in our common life that turns every disagreement into an argument, and every argument into a clash of cultures. So much of our politics has become a naked appeal to anger, fear and resentment. That leaves us worried about our nation and our future together.”

In an unscheduled stop Saturday at the Shanksville Volunteer Fire Department, Biden, too, alluded to Trump’s presidency as a period in which American democracy foundered under the weight of its divisions. The United States was founded on an idea that all men are created equal, Biden noted, as he frequently does in his speeches.

“It’s an idea, ‘we hold these truths,’ ” Biden said. “We never lived up to it, but we never walked away from it — except these last previous four years.”

Trump skipped the official remembrance ceremonies at all three sites Saturday, instead issuing several statements criticizing the Biden administration. A Trump spokeswoman told The Washington Post that he had the option of going to the ceremonies but chose to commemorate the day separately.

Trump is scheduled to provide commentary at a heavyweight boxing match on Saturday evening.

In a video message made public Saturday morning, Trump honored those who were killed in the 9/11 attacks — then blasted Biden’s withdrawal from Afghanistan last month. He ended the video with a call to “make America great again,” his campaign slogan.

On Saturday afternoon, Trump made a surprise visit to a New York City police precinct, where he baselessly alleged, as he has for months, that the 2020 presidential election was “rigged” against him and continued to bash Biden’s “gross incompetence” over his withdrawal from Afghanistan.

“It’s a sad day, it’s a very sad day for a lot of reasons,” Trump said at the police precinct. “And we just added to that reason last week because that never should have been allowed to happen, I have to say, and I’ve watched all the speeches, and nobody mentions it.”

Asked whether he planned to run for president again, Trump said it was an “easy question” but that “we’re not supposed to be talking about it yet.”

“I think you’re going to be happy,” he added. “Let me put it that way. I think you’re going to be very happy.”