Joe Walsh of Illinois, a former one-term House member, is set to announce he's challenging President Trump for the party's nomination for the 2020 election.

Walsh, 57, now a syndicated radio host and prolific tweeter, is expected to make the announcement this weekend, according to Politico. Walsh would face daunting odds against the sitting president, considering Trump's approval rating among Republican voters is consistently in the high 80s.

“If I’m to do it, it’s going to happen soon,” Walsh said. “I’ve been really surprised by the amount of anxiousness from people across the spectrum who want this president to have a challenge, because there’s just a real concern that he’s absolutely unfit.”

Walsh would join a seemingly growing field of GOP primary challengers to Trump. Former Massachusetts Gov. William Weld, the 2016 Libertarian Party vice-presidential nominee, previously announced his campaign. But Weld, 74, has little traction despite months of campaigning in New Hampshire. Former South Carolina governor and Congressman Mark Sanford is also eyeing a Republican primary challenge from the right, focused on deficit spending and fiscal discipline.

Maryland Gov. Larry Hogan earlier this year eyed a Republican primary challenge to Trump, but decided against running.

A Trump campaign spokesman responded to Walsh's expected announcement by telling the New York Times, it would end in "certain failure."

Walsh backed Trump for president in 2016 but has become a vociferous critic over the president's tweets, general temperament, and coziness with Russia, including what he called genuflecting to Russian President Vladimir Putin at a meeting in Finland.

“He lost me for good in Helsinki, when he stood in front of the world and said, ‘I believe Putin and I don’t believe my fellow Americans,’” Mr. Walsh stated.