Republican Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE (Ariz.) was caught on a hot mic Saturday warning that the Republican Party will be "toast" if it becomes the party of President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE and Roy Moore.

At a tax-reform event in Arizona on Saturday, Flake was caught on a live microphone by ABC affiliate KNXV bashing the president in a conversation with Mesa Mayor John Giles, a friend of Flake's.

ADVERTISEMENT

"If we become the party of Roy Moore and Donald Trump, we are toast," Flake is overheard saying.

Moore, a GOP candidate for the Senate in Alabama, has vowed to stay in the race despite mounting allegations of sexual misconduct involving teenage girls.

Giles, a moderate Republican who has been mayor of Mesa since 2014, is also heard on the recording making comments appearing to encourage Flake to mount a primary challenge against Trump in 2020.

"I am not throwing smoke at you, but you are the guy — just for fun, think about how much fun it would be — just to be the foil, you know, and point out what an idiot this guy is," Giles says, apparently referring to Trump. "Anyway, I hope you do it."

Flake has been a staunch critic of Trump, and announced in October that he would not seek reelection to his Senate seat in 2018.

In a speech on the Senate floor, he accused his party of abandoning its core principles.

"It is clear at this moment that a traditional conservative who believes in limited government and free markets, who is devoted to free trade, and who is pro-immigration, has a narrower and narrower path to nomination in the Republican party — the party that for so long has defined itself by belief in those things," Flake said during his speech.

"It is also clear to me for the moment we have given in or given up on those core principles in favor of the more viscerally satisfying anger and resentment," he added.