Rep. Justin Amash Justin AmashInternal Democratic poll shows tight race in contest to replace Amash Centrist Democrats 'strongly considering' discharge petition on GOP PPP bill On The Trail: How Nancy Pelosi could improbably become president MORE made headlines this weekend when he broke with his party to become the first Republican lawmaker to accuse President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE of "impeachable conduct." But the Michigan conservative has a history of bucking GOP leaders.

Amash tweeted on Saturday that the president's actions to potentially obstruct 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 investigation into Russian election interference warrant impeachment proceedings by the House.

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He also accused Attorney General William Barr Bill BarrHarris faces pivotal moment with Supreme Court battle Hillicon Valley: DOJ proposes tech liability shield reform to Congress | Treasury sanctions individuals, groups tied to Russian malign influence activities | House Republican introduces bill to set standards for self-driving cars McCarthy threatens motion to oust Pelosi if she moves forward with impeachment MORE of "deliberately misrepresenting" Mueller's report on the investigation's findings.

This is not the first time Amash has stood out in the Republican Party by criticizing Trump or other top party officials, something the president highlighted when he hit back on Twitter on Sunday.

....he would see that it was nevertheless strong on NO COLLUSION and, ultimately, NO OBSTRUCTION...Anyway, how do you Obstruct when there is no crime and, in fact, the crimes were committed by the other side? Justin is a loser who sadly plays right into our opponents hands! — Donald J. Trump (@realDonaldTrump) May 19, 2019

Amash, a member of the Freedom Caucus and the Liberty Caucus, was elected to the House in 2010 as part of the anti-establishment libertarian wave that returned control of the lower chamber to Republicans.

He quickly made a name for himself by voting no on a GOP-backed government funding measure because it did not do enough to cut spending, as well as citing constitutionality issues to abstain from several other votes.

In 2012, he was removed from a committee post by then-Speaker John Boehner John Andrew BoehnerLongtime House parliamentarian to step down Five things we learned from this year's primaries Bad blood between Pelosi, Meadows complicates coronavirus talks MORE (R-Ohio) for challenging his leadership.

Amash then backed a failed coup attempt to depose Boehner John Andrew BoehnerLongtime House parliamentarian to step down Five things we learned from this year's primaries Bad blood between Pelosi, Meadows complicates coronavirus talks MORE.

“We have to stand for something and we have to present a clear message to the American people and that hasn't happened,” Amash said at the time.

As soon as Trump won the Republican nomination for president, Amash made clear he was not in support of the New York real estate mogul, who he said had an "extra-constitutional" view of presidency.

“He seems to believe that government works like a business and he is the CEO of the business, and that is not how it works,” Amash told The Hill in December of 2016, following Trump's surprise election. “We have separate branches, checks and balances, federalism."

Constitutionality has been a key part of Amash's disagreements with Trump since the president's inauguration.

He has also been critical of the Trump administration's policies, including its attempt at repealing and replacing ObamaCare.

"While I've been in Congress, I can't recall a more universally detested piece of legislation than this GOP health care bill," Amash tweeted in March 2017.

The bill was approved by the House and defeated in the Senate, but only after the initial version was pulled after opposition from Amash, among others.

Just months into Trump's term, Amash said the president, who advertised himself as an outsider, had merged with the Washington swamp he had pledged to drain, coining the hashtag #Trumpstablishment.

After Trump fired FBI Director James Comey James Brien ComeyDemocrats fear Russia interference could spoil bid to retake Senate Book: FBI sex crimes investigator helped trigger October 2016 public probe of Clinton emails Trump jabs at FBI director over testimony on Russia, antifa MORE, Amash joined the ranks of Democrats calling for an independent investigation into Russia’s possible ties to the Trump administration.

“My staff and I are reviewing legislation to establish an independent commission on Russia. The second paragraph of this letter is bizarre,” Amash tweeted in May 2017, referring to the paragraph in Trump’s letter to Comey that stated “I greatly appreciate you informing me, on three separate occasions, that I am not under investigation.”

He was also one of the first Republicans to suggest impeachment was on the table in May 2017 after Comey wrote a memo indicating that Trump urged the FBI to drop the investigation into former national security adviser Michael Flynn.

Last June, Amash and Trump got into a public argument over the president's attacks of then-Rep. Mark Sanford Mark SanfordOn The Money: Business world braces for blue sweep | Federal Reserve chief to outline plans for inflation, economy | Meadows 'not optimistic' about stalemate on coronavirus deal Trump critic Sanford forms anti-debt advocacy group Republicans officially renominate Trump for president MORE (R-S.C.) during a closed-door meeting.

Trump claimed that Republicans "applauded and laughed loudly" when he called Sanford a "nasty guy" in a meeting that the South Carolina Republican, an outspoken critic of the president's rhetoric, missed because of a flight delay.

Amash disputed Trump's claim that the comments were well received.

"House Republicans had front row seats to @POTUS’s dazzling display of pettiness and insecurity. Nobody applauded or laughed. People were disgusted," Amash tweeted.

That same month, the Michigan lawmaker criticized Trump picking Brett Kavanaugh Brett Michael KavanaughHarris faces pivotal moment with Supreme Court battle Poll: 59 percent think president elected in November should name next Supreme Court justice Feinstein 'surprised and taken aback' by suggestion she's not up for Supreme Court fight MORE as his Supreme Court nominee because of a 2015 opinion written by nominee while serving on the U.S. Court of Appeals for the D.C. Circuit, that found “the Government’s metadata collection program is entirely consistent with the Fourth Amendment."

The libertarian was one of eight Republicans in the House last fall to vote against a funding package that included $5.7 billion in funding for Trump’s border, calling it a "massive, wasteful spending bill."

He was then the only Republican to cosponsor a bill to block Trump's emergency declaration to secure funding for a wall after Congress refused to budge on the issue.

"A national emergency declaration for a non-emergency is void. A prerequisite for declaring an emergency is that the situation requires immediate action and Congress does not have an opportunity to act. @POTUS @realDonaldTrump is attempting to circumvent our constitutional system," Amash tweeted following the president's declaration.

Amash has said that he would not rule out challenging Trump in the 2020 election as the Libertarian Party's candidate.

Amash's office did not immediately respond to a request for comment for this story.