Outgoing Sen. Jeff Flake (R-AZ) said on Sunday that President Donald Trump’s behavior is “inviting” a Republican or Independent challenger in 2020.

And he’s not opposed to being the one to step up to that plate.

“I haven’t thought that deeply about it,” Flake, a longtime vocal critic of Trump, said Sunday during an interview on ABC’s “This Week” when asked about a potential presidential bid. “But I do believe if the President is running for reelection, if he continues on the path that he’s on, that that’s gonna leave a huge swath of voters looking for something else.”

Trump’s political discourse and alienation of Republicans outside his base will likely prompt a challenger from his own party in 2020, especially if Democrats back a “far left” candidate, Flake said.

“I do worry, that in the future we’ll be faced with a President Trump running for reelection on one side, drilling down hard on a diminishing base and on the other side you might have you know somebody like Bernie Sanders or Elizabeth Warren on the far left of the Democratic Party,” he said. “That leaves a huge swath of voters in the middle, that may be looking for something else.”

In a fiery speech from the Senate floor in October, Flake announced his plans to retire when his term is up. At the time, the Arizona senator said his decision was based solely on a desire to not be “complicit” in the age of Trump.

“Reckless, outrageous, and undignified behavior has become excused and countenanced as ‘telling it like it is,’ when it is actually just reckless, outrageous and undignified,” he said in October. “And when such behavior emanates from the top of our government, it is something else: It is dangerous to a democracy.”

Flake did not vote for Trump in the 2016 election and has been articulate about his contempt for the President for months. The senator published a book this summer, criticizing conservatives in his party for backing Trump.

Watch a clip from the ABC interview below: