Thirteen former Trump White House officials signed an open letter backing up former Trump chief of staff John Kelly, who told the New York Times that Trump fits the definition of a fascist.

“We applaud General Kelly for highlighting in stark details the danger of a second Trump term. Like General Kelly, we did not take the decision to come forward lightly,” the letter said. “We are all lifelong Republicans who served our country. However, there are moments in history where it becomes necessary to put country over party. This is one of those moments.”

Politico was first to report on the letter.

The letter, released by the Harris campaign, is signed by former officials including former press secretary Stephanie Grisham, former chief of staff at the Department of Homeland Security Miles Taylor, and Olivia Troye, former national security adviser to Mike Pence. All three former Trump administration officials have become high-profile critics of his after his presidency ended.

Troye and Grisham spoke at the Democratic National Convention this year. Troye was also one of the signatories of a letter in August from over 200 Republican officials backing Vice President Kamala Harris for president.

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In his interview with the Times, released Tuesday, Kelly also said he observed Trump on multiple occasions praising Adolf Hitler. His comments came on the same day the Atlantic reported that Trump said he wished he had generals like Hitler.

In their letter, the former Trump officials said Kelly’s claims were “disturbing and shocking.” They added that “because we know Trump and have worked for and alongside him, we were sadly not surprised by what General Kelly had to say. This is who Donald Trump is.”

Trump on Thursday denied ever having said positive things about Adolf Hitler, including that he needed “the kind of generals that Hitler had.”

The Harris campaign has been highlighting Kelly’s comments about his former boss, releasing a new ad on Thursday using Kelly’s audio published by The New York Times.

In remarks Wednesday, Harris said that Kelly's claims are "a window into who Donald Trump really is, from the people who know him best, from the people who worked with him side by side in the Oval Office and in the Situation Room."

She added that "in a second term, people like John Kelly would not be there to be the guardrails against his propensities and his actions."

A Harris campaign official told NBC News that the campaign’s focus group of undecided voters this week found Kelly credible and non-partisan, leading some to further question voting for Trump.