Former senator Jeff Flake (R-Ariz.) said in an op-ed published Monday that President Trump’s actions warrant impeachment and urged fellow Republicans not to support his reelection if he remains in office.

In the piece for The Washington Post, Flake cited President Trump’s July call with Ukrainian President Volodymyr Zelensky, in which Trump repeatedly urged Zelensky to investigate former vice president Joe Biden and his son at a time when the White House had suspended military aid to Ukraine.

“We have learned from a whistleblower that the president has abused the power of his office to pressure a foreign government to go after a political opponent,” Flake wrote. “A rough transcript of the telephone call has removed all ambiguity about the president’s intent.”

Most Republicans in Congress are rallying around Trump, as House Democrats aggressively move forward with an impeachment inquiry.

Flake argued that impeachment is a difficult call.

“I fear that, given the profound division in the country, an impeachment proceeding at such a toxic moment might actually benefit a president who thrives on chaos. Disunion is the oxygen of this presidency,” Flake wrote.

He said that, by contrast, a decision not to support Trump’s reelection is easy — although he acknowledged that it could come with consequences.

Flake referenced his own decision to retire last year after becoming an outspoken critic of Trump and seeing his popularity in Arizona decline.

“I would have preferred to represent the citizens of Arizona for another term in the Senate,” Flake wrote. “But not at the cost of supporting this man. A man who has, now more than ever, proved to be so manifestly undeserving of the highest office that we have. . . . My fellow Republicans, it is time to risk your careers in favor of your principles. Whether you believe the president deserves impeachment, you know he does not deserve reelection.”

Last week, speaking on a Slate podcast from the Texas Tribune Festival, Flake claimed that at least 35 Republican senators would vote for Trump’s impeachment if they could do so privately.

“Anybody who has sat through two years, as I have, of Republican luncheons realizes that there’s not a lot of love for the president,” he said later during an interview with NPR.