Monday on his nationally syndicated radio program, conservative commentator Mark Levin blasted Rep. Justin Amash’s (R-MI) recent views on President Donald Trump and impeachment, referring to the libertarian-leaning congressman as “a Benedict Arnold against the Constitution.”

“What Justin Amash did was a disgrace. He’s a Benedict Arnold,” Levin began, according to the Conservative Review. “He’s a Benedict Arnold against the Constitution,” the radio host added. “While he poses to be for the Constitution. While he poses as a purist of the Constitution, he’s no damn such thing.”

Amash is under fire after accusing President Trump of committing “impeachable” offenses stemming from special counsel Robert Mueller’s report on now-debunked collusion between the Trump campaign and Russia during the 2016 presidential election. The Michigan Republican also claimed Attorney General William Barr misrepresented Mueller’s findings.

“Contrary to Barr’s portrayal, Mueller’s report reveals that President Trump engaged in specific actions and a pattern of behavior that meets the threshold for impeachment,” Amash wrote on Twitter Saturday. He then said that Mueller’s findings “identifies multiple examples of conduct satisfying all the elements of obstruction of justice, and undoubtedly any person who is not the president of the United States would be indicted based on such evidence.”

Levin went on to accuse Amash of being a hypocrite by smearing the attorney general, while claiming to uphold the constitution.

[T]his man stands up and pretends that he’s defending the Constitution by calling Bill Barr a liar, by saying the president of the United States has demonstrated he ought to be impeached!” Levin said.

The Michigan lawmaker’s remarks have been met with blowback from leading Republicans, including President Trump himself. “Never a fan of @justinamash, a total lightweight who opposes me and some of our great Republican ideas and policies just for the sake of getting his name out there through controversy, the president tweeted on Sunday. “Justin is a loser who sadly plays right into our opponents [sic] hands!”Appearing Sunday on the Fox News Channel, House Minority Leader Kevin McCarthy (R-CA ) dismissed Amash as nothing more than an attention-seeker. “You’ve got to understand Justin Amash. He’s been in Congress quite some time,” McCarthy said. “I think he’s asked one question in all the committees that he’s been in. He votes more with Nancy Pelosi than he ever votes with me. It’s a question whether he’s even in our Republican conference as a whole.”

In the wake of Amash’s remarks, Michigan State Rep. Jim Lower (R) on Monday announced he will mount a primary challenge against the congressman.

“Congressman Justin Amash tweets yesterday calling for President Trump’s impeachment show how out of touch he is with the truth and how out of touch he is with people he represents,” Lower told the Detroit Free Press. “He must be replaced and I am going to do it.”