GOP Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeHow fast population growth made Arizona a swing state Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden MORE (Ariz.) hit back at President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE on Tuesday, saying the president was “wrong” to suggest he could run special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE’s Russia probe.

"He's wrong,” Flake told reporters at the Capitol. “He can't and he ought to stop trying to undermine it as well. It's unseemly, it really is — these statements calling people ‘thugs’ and ‘lowlifes.’”

He added that Trump’s comments on trying to control the Russia probe takes his rhetoric to “another level.”

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“I am concerned, I think all of us are, that he seems to be stepping it up lately,” said Flake, who is retiring in early 2019.

Trump said during an interview with Reuters this week that if he wanted to he could “run” Mueller’s investigation into potential collusion between Moscow and the Trump campaign.

“I can go in, and I could do whatever — I could run it if I want,” Trump said. “But I decided to stay out.”

“I’m totally allowed to be involved if I wanted to be,” he added. "So far, I haven’t chosen to be involved. I’ll stay out.”

Trump later tweeted that Mueller and his team are “thugs” and a “national disgrace.”

The president’s rhetoric on Mueller’s investigation has sparked backlash on Capitol Hill. Senate Republicans, while publicly urging the special counsel to wrap up his probe before the November midterm elections, have been reluctant to directly criticize Mueller.

Flake added on Tuesday that Trump should just “stay out” of interfering in the investigation.

"If you're not worried about anything then let them finish their work,” he said.