WASHINGTON — More than 100 former national security officials from Republican administrations and former Republican members of Congress endorsed Vice President Kamala Harris, the Democrats’ presidential candidate, on Wednesday after concluding that their party’s nominee, former President Donald Trump, is “unfit to serve again as president.”

In a letter to the public, the Republicans, including both vocal longtime Trump opponents and others who had not endorsed Joe Biden in 2020, argued that while they might “disagree with Kamala Harris” on many issues, Trump had demonstrated “dangerous qualities.” Those include, they said, “unusual affinity” for dictators like Vladimir Putin of Russia and “contempt for the norms of decent, ethical and lawful behavior.”

“As president,” the letter said, “he promoted daily chaos in government, praised our enemies and undermined our allies, politicized the military and disparaged our veterans, prioritized his personal interest above American interests and betrayed our values, democracy and this country’s founding documents.”

The letter condemned Trump’s incitement of the mob attack on the Capitol on Jan. 6, 2021, aimed at allowing him to keep power after losing an election, saying “he has violated his oath of office and brought danger to our country.” It quoted Trump’s former vice president, Mike Pence, who has said that “anyone who puts himself over the Constitution should never be president of the United States.” Pence has not endorsed Harris.

The letter came not long after former Vice President Dick Cheney and his daughter former Rep. Liz Cheney of Wyoming both said they would vote for Harris. Democrats featured anti-Trump Republicans at their convention in August, including former Rep. Adam Kinzinger of Illinois.

The 111 signatories included former officials under Presidents Ronald Reagan, George H.W. Bush or George W. Bush. Many of them had previously broken with Trump, including two former defense secretaries, Chuck Hagel and William Cohen; Robert Zoellick, a former president of the World Bank; former CIA directors Michael Hayden and William Webster; and a former director of national intelligence, John Negroponte.

But a number of Republicans who did not sign a similar letter on behalf of Biden in 2020 signed the one for Harris this time, including several former House members, such as Charles Boustany of Louisiana, Barbara Comstock of Virginia, Dan Miller of Florida and Bill Paxon of New York.