Republican U.S. Rep. Justin Amash reaffirmed his assertion that President Donald Trump committed impeachable acts, not backing down from weekend comments that drew attacks from the president and encouraged a Republican primary challenger to step forward.

People who say there were no underlying crimes and therefore the president could not have intended to illegally obstruct the investigation—and therefore cannot be impeached—are resting their argument on several falsehoods: — Justin Amash (@justinamash) May 20, 2019

Amash, R-Cascade Township, became the first Republican congressman to support impeachment proceedings based on findings in U.S. Special Counsel Robert Mueller’s investigation into 2016 election interference. The investigation did not establish Trump or any of his aides coordinated with Russia in its efforts to influence the 2016 election, but left open the question of whether Trump obstructed justice.

Amash said the Mueller report reveals Trump’s actions “meet the threshold for impeachment," in a series of tweets outlining his conclusions. Amash said any person who is not the president of the United States would “undoubtedly” be indicted based on evidence in the report.

Trump responded the following day, also on Twitter, calling Amash “a loser” and “total lightweight” who is attempting to call attention to himself. Michigan GOP Chair Laura Cox also slammed Amash for what she saw as a “desperate attempt to grab headlines advance his own presidential ambitions."

“If he actually read the biased Mueller Report, ‘composed’ by 18 Angry Dems who hated Trump, he would see that it was nevertheless strong on NO COLLUSION and, ultimately, NO OBSTRUCTION," Trump tweeted Sunday, May 19.

Amash published a new series of tweets Monday afternoon to clarify his position and push back against narratives defending Trump. Amash again concluded that the president is guilty of obstructing justice.

The Mueller investigation revealed “many crimes,” Amash said, but an underlying crime isn’t required for someone to illegally obstruct the investigation.

“Prosecutors might not charge a crime precisely because obstruction of justice denied them timely access to evidence that could lead to a prosecution," Amash said. "If an underlying crime were required, then prosecutors could charge obstruction of justice only if it were unsuccessful in completely obstructing the investigation. This would make no sense.”

The Michigan Republican said Trump could not have known whether there were legitimate crimes being investigated. Amash also highlighted the phrase “high crimes and misdemeanors,” included in a portion of the Constitution outlining impeachment, saying it remains undefined but implies the inclusion of “any conduct that violates the public trust.”

In his first round of tweets, Amash said Attorney General William Barr “deliberately misrepresented Mueller’s report,” and “few members of Congress” have read the 488-page document.

Amash, now serving his fifth term in the House, said earlier this year that he “can’t rule out” running for president as a Libertarian. He hasn’t declared any concrete intentions for 2020, but told MLive.com in a March interview that “someone” needs to run for president who values integrity over party loyalty.

“We’ve witnessed members of Congress from both parties shift their views 180 degrees -- on the importance of character, on the principles of obstruction of justice -- depending on whether they’re discussing Bill Clinton or Donald Trump,” Amash tweeted Saturday.

The Michigan Republican has gained a national following as one of the only congressmen who isn’t afraid to buck the Republican line, often going to toe to toe with the party’s biggest star.

State Rep. Jim Lower, R-Greenville, rose to challenge Amash in the 2020 Republican primary two days after the initial tweets were published. Lower said Amash’s comments show "how out of touch he is with the truth and how out of touch he is with people he represents.”

Lower, 30, who was elected to the Michigan House of Representatives in 2016, said he originally planned to announce his candidacy on July 4.

Amash is chair of the House Liberty Caucus and helped found the House Freedom Caucus. Both were formed to oppose executive overreach and government spending.