"I realized I probably hadn't said anything that I hadn't said in public," Flake said in an interview on KFYI radio in Phoenix.
He continued, "And it was the case. I've been saying for anyone who would listen that we are in trouble as a party if we continue to follow both Roy Moore and Donald Trump. I just don't think that is the direction for the party."
Flake has been an outspoken critic of Trump's behavior and his approach on a few issues like immigration and trade, and he has disavowed Alabama Republican Senate nominee Roy Moore.
At a town hall event last week in Mesa, Arizona, Flake left a microphone on his lapel as he left the stage. The microphone captured Flake saying he thought if the GOP becomes "the party of Roy Moore and Donald Trump, we are toast."
Mesa Mayor John Giles was heard making comments apparently encouraging Flake to challenge Trump for the presidency in 2020 and said Flake would be able to "point out what an idiot" Trump is.
on Sunday, saying Flake was caught "saying bad things about your favorite President" and anticipated Flake would vote against the Senate GOP tax cut proposal.
Flake said in the interview Monday that the mayor seeming to call Trump "an idiot" was unfortunate and went against his call for more civility in public life. He said, however, that the mayor thought he was speaking privately and did not mean to air a public insult.
"I doubt the mayor would have said that in public and neither would I and neither would you," Flake said. "In private moments, I think we all probably talk differently."
He said he was not "focused" on a 2020 bid and that he was continuing to do his work in the Senate, including tax reform.
Flake did not commit to supporting the tax bill and said he was balancing his desire to establish reform with his concerns about raising the deficit.
"I can tell you one thing, what the President says or does or feels has nothing whatsoever to do with how I will vote on that tax bill," Flake said.