Sen. Jeff Flake (R-Ariz.) speaks with reporters on Capitol Hill in Washington in December. (J. Scott Applewhite/AP)

Former senator Jeff Flake (R-Ariz.) on Tuesday ruled out a primary challenge to President Trump next year, saying he doesn’t see “a path right now” but still hopes another member of his party steps forward to run.

“I have always said that I do hope that there is a Republican who challenges the president in the primary,” Flake said during an appearance on “CBS This Morning.” “I still hope that somebody does, but that somebody won’t be me. I will not be a candidate.”

Before retiring from the Senate in January, Flake had been one of Trump’s more vocal Republican critics, accusing him at one point of not demonstrating “grown-up leadership.”

Flake stoked speculation about a 2020 challenge to Trump in March, when he traveled to New Hampshire, the nation’s first primary state, to deliver an address to a crowd of business leaders and political activists. In his speech, he decried the “degradation of the United States and her values” by the current occupant of the White House.

Flake said during his CBS appearance, however, that he has a difficult time envisioning prevailing against Trump.

“There really isn’t a path right now that I could see, certainly not unless you’re willing to be out there already, raising a lot of money and basically living on the road right now,” he said.

He also cited the strong backing of Trump by the Republican National Committee.

At a meeting last week, members approved by voice vote a resolution hailing Trump as a “pragmatic, energized President who shares and understands the will of the American people.”

Some other Republicans have not ruled out a 2020 challenge to Trump, including former Ohio governor John Kasich and Maryland Gov. Larry Hogan.

In recent years, Trump had also periodically taken aim at Flake. In June, Trump took to Twitter to question how Flake could consider running for another office given low poll numbers in his own state.

“Let’s face it, he’s a Flake!” Trump said.