WASHINGTON — A day after Michigan U.S. Rep. Justin Amash became the first Republican congressman to say President Donald Trump committed impeachable offenses, the president attacked him on Twitter calling him a "loser" and "a total lightweight."

""Never a fan of (Amash) … who opposes me and some of our great Republican ideas and policies just for the sake of getting his name out there through controversy." wrote Trump in a short series of tweets.

"If he actually read the biased Mueller Report … he would see that it was nevertheless strong on NO COLLUSION and, ultimately, NO OBSTRUCTION."

The president has maintained in the aftermath of the report issues by Special Counsel Robert Mueller that he was completely vindicated. But, despite his comments to the contrary, the report left open the possibility he engaged in obstruction of justice, only saying that, as president, he couldn't be indicted on such a charge.

On Saturday evening, Amash, R-Cascade Township — who has sparred with the president before and who some reports say may consider a run for the presidency — went on Twitter to say he had read the entire Mueller report and reached a different conclusion than the president other Republicans.

Amash sharply criticized U.S. Attorney General William Barr, who concluded after reading the report that Trump — his boss — neither colluded with Russians effort to affect the 2016 election or committed obstruction in attempting to thwart the investigation.

Amash said that "Contrary to Barr’s portrayal, Mueller’s report reveals that President Trump engaged in specific actions and a pattern of behavior that meet the threshold for impeachment."

"In fact, Mueller’s report 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," said Amash, who is a lawyer.

Amash also concluded that many of his colleagues in both parties hadn't read the report and were only making comments based on partisan considerations.

Amash didn't immediately reply to an inquiry from the Free Press for further comment on Sunday.

Immediately following Amash's tweets on Saturday, U.S. Rep. Rashida Tlaib, D-Detroit, suggested that Amash could join her resolution calling for an investigation into whether Trump should be impeached.

Michigan Democratic consultant Joe DiSano tweeted, "I’ve given @justinamash a lot of guff over the years. … But this move … guarantees a mid-tier challenger who will be funded at the highest level. Takes guts to wreck summer '19 and '20. But it’s worth it."

Republicans denounced Amash's remarks.

State Rep. Jim Lower, R-Cedar Lake, said on Twitter, "This cannot go unchallenged! … I will have a major announcement regarding (Amash's congressional district) this week," raising the suggesting that he might challenge Amash, a five-term incumbent.

Republican National Committee chairwoman Ronna McDaniel — who lives in Michigan and is a former state party chair — said it was "sad to see (Amash) parroting the Democrats’ talking points on Russia."

"The only people still fixated on the Russia collusion hoax are political foes of @realDonaldTrump hoping to defeat him in 2020 by any desperate means possible," she said.

The Michigan Republican Party did not issue a statement on Amash’s tweets about Trump.

But Chairwoman Laura Cox issued the following statement via her personal twitter account:

“While President Trump’s leadership has led to the strongest economy in a generation, Justin Amash has opposed his ‘America First’ agenda every step of the way. Now in a desperate attempt to grab headlines and advance his own presidential ambitions, Amash is peddling a narrative that has repeatedly been proven false. Shameful.”

U.S. Senator and former Republican presidential candidate Mitt Romney of Utah on Sunday told CNN that Amash's comments were courageous but said he disagrees that Trump's conduct has met the "threshold for impeachment."

"My own view is that Justin Amash has reached a different conclusion than I have. I respect him, I think it's a courageous statement," Romney told CNN's Jake Tapper on "State of the Union."

"The American people just aren't there," he added. "The Senate is certainly not there, either."

It is not the first time Trump and Amash have sparred. Two years ago, Trump and his advisers went after Amash for failing to support a proposal by House Republican leaders to rewrite the Affordable Care Act. Amash, however, didn't support the Democratic position — he wanted government even less involved in health care than the GOP plan.

Also, two years ago Amash said that if remarks by former FBI Director James Comey that Trump encouraged him to drop an investigation into former National Security Adviser Michael Flynn were true, it could warrant impeachment.

Ultimately, any threats to try to put a serious primary challenger up against Amash evaporated and he easily won re-election in 2018.

Rep. Amash couldn't be reached for comment and didn't immediately react to Trump's tweets.

More on freep.com:

Amash-Trump feud continues in wake of Obamacare loss

Tlaib submits measure calling for impeachment probe into President Trump

Contact Todd Spangler attspangler@freepress.com. Follow him on Twitter@tsspangler. Read more onMichigan politics and sign up for ourelections newsletter. Staff writer Kathleen Gray contributed to this story.