Editor's Note: (This story was originally published on March 10, 2019, after Michigan Republican Rep. Justin Amash declined to rule out a 2020 challenge to President Donald Trump. It has been updated to reflect his July 4 departure from the Republican Party. )

Washington(CNN) For most Republicans, life in the House minority is a big change. But for Rep. Justin Amash, in a sense, it's more of the same.

"It's just a different set of people doing the wrong thing," the Michigan Republican said in a March interview with CNN.

Amash came to Congress with the Tea Party wave in 2010, and although Republicans controlled the House for the entirety of his congressional career until a few months ago, Amash has long been the odd man out.

His firm libertarian stances on foreign policy, surveillance and federal spending put him in an awkward position with many in his own party. And two years into Donald Trump's presidency, Amash appears lonelier than ever.

On Thursday he announced he would break with the Republican Party, decrying partisanship in Washington.

"Today, I am declaring my independence and leaving the Republican Party," Amash wrote in a Washington Post op-ed Thursday morning. "No matter your circumstance, I'm asking you to join me in rejecting the partisan loyalties and rhetoric that divide and dehumanize us. I'm asking you to believe that we can do better than this two-party system — and to work toward it. If we continue to take America for granted, we will lose it."

His closest allies -- conservatives who routinely sparred with the GOP establishment in the past -- have coalesced behind Trump even as his political and legal woes have mounted, with Republican lawmakers now marching in lock-step behind the President even on issues they historically haven't supported, like shutting down the government. But that's not Amash's style.

And his fierce independence could be a sign of trouble for Republicans in the future: In an interview with CNN's Jake Tapper, Amash recently declined to rule out running for president as a libertarian in 2020. "I would never rule anything out," said Amash. "That's not on my radar right now, but I think that it is important that we have someone in there who is presenting a vision for America that is different from what these two parties are presenting."

It's a far cry from the turn Amash's associates have taken in the Trump age.

The Michael Cohen hearing

The divide was clearer than ever during a February oversight hearing with former Trump attorney Michael Cohen. While most Republicans on the panel stuck to Ohio Rep. Jim Jordan's strategy of attacking Cohen's character and playing defense for the President, Amash asked sharp questions designed to draw out information.

"What is the truth that you know President Trump fears most?" he asked. Amash told CNN in an interview after the hearing that he gave Jordan advance warning his questioning would be tough.

"Justin's a great American," Jordan said when asked about the episode.

Jordan and Amash were both founding members of the House Freedom Caucus, a group of hardline conservatives who preached a focus on cutting government spending and opening up congressional procedure, and clashed with party leaders over it. The three dozen members played a key role in former House Speaker John Boehner's resignation in 2015, and the caucus was instrumental in shaping the House-led GOP effort to repeal Obamacare, which became a centerpiece of Trump's first-year agenda -- though it failed to pass through the more moderate Senate.

But the Freedom Caucus of 2019 is a different story.

Wielding considerably less power in a Democratic House, the caucus is more recognizable today as home to some of Trump's staunchest defenders. Jordan and current chairman Rep. Mark Meadows regularly make headlines with their ardent efforts to push back on investigations into the White House and Russian interference in the 2016 election.

Every day, their allegiance to the President seems to reach new heights, and every day, Amash's position among his allies seems a little more strained.

"From the time the President was elected, I was urging them to remain independent and to be willing to push back against the President where they thought he was wrong," said Amash. "They've decided to stick with the President time and again, even where they disagree with him privately."

The emergency powers vote

Amash was the sole member of the caucus to vote against Trump's use of emergency powers to seize funds for his long-desired wall along the southern border, even though the Freedom Caucus was known for lambasting President Barack Obama's executive maneuvering to get around Congress.

"In some sense you've delegitimized objections to the President," Amash said of his peers. "You've built up such credibility for him that you just can't challenge him anymore."

Asked if he'd thought about leaving the Freedom Caucus in recent months, the congressman admitted he has been "disenchanted" enough to consider it at times. But he said having close partners to work with on issues he cares about has kept him from calling it quits.

Still, the relationship has evolved.

Leading up to the 2018 election, Amash started to feel like the group wasn't going to turn around. Since then, he hasn't been attending all of the meetings like he used to, going only "infrequently," he told CNN.

"I came to a meeting and really gave them a dramatic speech about what my concerns were and what we needed to do as a group and how we were losing sight of our purpose and our principles," Amash recalled. "And that was sort of it."

Tension built as Amash regularly argued for the group to return to a focus on opening up the legislative process. In recent years, it has become harder and harder for rank-and-file members to have a say in lawmaking. Leaders in both parties opt for a top-down approach, rejecting the idea of allowing a robust amendments process. When the Senate was debating the GOP health care bill, only a small handful of senators actually knew what would be included in the bill — even up until the final hours before the vote. And the House recently experienced its most closed session in history under now-retired House Speaker Paul Ryan.

A changing caucus

The question of whether to prioritize process or policy has plagued the Freedom Caucus since its inception, and divisions have only heightened in the Trump age. It hasn't helped that Amash has lost key allies like Raul Labrador, the Idaho lawmaker who left Congress last year to run unsuccessfully for governor of his state, and Mark Sanford, who lost his South Carolina primary to a more Trump-friendly opponent in 2018.

Yet Amash reiterated his Freedom Caucus colleagues remain some of his closest friends in Congress.

"They are good, kind people," he said. "I may have my disagreements with some of the current approach, but I'd still take them over pretty much anyone in Congress."

And members who differ with Amash's stance say he still brings a helpful perspective.

"Justin, like all of us, is just looking for a way to be the most effective and efficient he can be," Arizona Rep. Andy Biggs said. "When we're debating, he engages in debate and offers a ton of valuable comments and I think that's invaluable for all of us."

Amash has the rhetorical style of someone who really enjoys arguing for the sake of arguing but also benefits from fiercely believing what he says. He also has a wry sense of humor.

Soon after inauguration day in early 2017, Trump signed a travel ban targeting six majority Muslim countries. Amash — whose mother is a Syrian immigrant and whose father came to America as a Palestinian refugee in 1956 — opposed the executive order. In the immediate aftermath of the ban, protestors flocked to airports, where travelers were stranded.

At the height of the outcry, Amash excused his lateness to a Freedom Caucus meeting one night with a joke at the administration's expense, according to one attendee who told CNN about the incident at the time. "Hey guys. Sorry I'm late," he said. "The travel ban got me held up at the airport — they're screening all the Syrians."

Half of the room was amused by the quip. The other half — not so much. It was memorable enough that a lawmaker who also attended the meeting still recalled the episode more than two years later.

To his closest friends in Congress, Amash's ability to call out his own side is part of his charm.

"Justin Amash is probably one of the most, if not the most consistent and honorable members of Congress that I met in the eight years I was there," Labrador, the former Idaho representative, said. "He always outlined what he believes in, why he believes in the things that he does and why he makes the decisions that he makes."

It's not clear what's next for Amash, whether another term in the House or something new. He admits he's thought about everything from breaking away from the GOP to launching a presidential bid.

"I never stop thinking about these sorts of things," he told CNN. "It's not because I have any immediate plans or anything like that, but I never stop thinking about those things because there is a big problem with the current two-party system we have, and someone has to shake it up."

"Now, is it possible for anyone to shake it up and make a difference?" he added. "I don't know."