• More than 100 Republican former lawmakers and officials endorsed Democratic presidential nominee Kamala Harris.
• The group argued that former President Donald Trump, their own party's nominee, is "unfit to serve again."
• The group includes former Trump administration officials, as well as officials who served under former Presidents Ronald Reagan, George H.W. Bush and George W. Bush.

More than 100 Republican former lawmakers and officials endorsed Democratic presidential nominee Vice President Kamala Harris in a letter, while warning that their own party's candidate, former President Donald Trump, is "unfit to serve again."

In the letter, shared by the Harris campaign Wednesday, 111 former national security and foreign policy officials said that despite their disagreements with the vice president's policies, "we believe that she possesses the essential qualities to serve as President and Donald Trump does not."

They decried Trump for sowing "daily chaos in government" during his first term in office, arguing that he put his personal interests before the country's and "violated his oath of office" by inciting the Jan. 6, 2021, riot at the U.S. Capitol.

The group, which includes former Trump administration officials as well as officials who served under former Presidents Ronald Reagan, George H.W. Bush and George W. Bush, also warned of Trump's "susceptibility to flattery" by foreign leaders.

"He is unfit to serve again as President, or indeed in any office of public trust," they said in the letter, which The New York Times first reported earlier Wednesday.

The signatories include former CIA and FBI director William Webster, former director of national intelligence John Negroponte, and former U.S. trade representatives Carla Hills and Robert Zoellick.

They acknowledged many Republicans' concerns about Harris and preference for Trump. "But any potential concerns pale in comparison to Donald Trump's demonstrated chaotic and unethical behavior and disregard for our Republic's time-tested principles of constitutional governance," they argued.

"His unpredictable nature is not the negotiating virtue he extols. To the contrary, in matters of national security, his demeanor invites equally erratic behavior from our adversaries, which irresponsibly threatens reckless and dangerous global consequences."

Eight former members of Congress also endorsed the Democratic ticket of Harris and Minnesota Gov. Tim Walz in the letter.

Wednesday's letter marks the latest addition of GOP support for Harris, who has sought to appeal to more moderate voters and conservatives who may be disillusioned with Trump.

Her campaign in August launched "Republicans for Harris," touting endorsements from more than two dozen ex-Trump officials and other GOP members.

In early September, Harris won the support of nearly 90 corporate leaders, including former 21st Century Fox CEO James Murdoch, Snap Chairman Michael Lynton and Yelp co-founder Jeremy Stoppelman.

Dick Cheney, the vice president to George W. Bush, announced the same month that he would vote for Harris. His daughter, former GOP Rep. Liz Cheney, is one of Trump's loudest conservative critics.

Meanwhile, Trump's former vice president, Mike Pence, reaffirmed Tuesday that he would not endorse any presidential candidate in the 2024 election.

Pence specifically referenced the events of Jan. 6, 2021, when Trump pressured his then-vice president to reject the lawful Electoral College results showing President Joe Biden won the 2020 election. After Pence rebuffed Trump, a mob of the then-president's supporters stormed the Capitol and derailed the election certification.

Wednesday's letter included a quote from Pence: "Anyone who puts himself over the Constitution should never be President of the United States."