When President Donald Trump appointed Justice Amy Coney Barrett to the Supreme Court weeks before the 2020 election, outraged liberals attacked her as a right-wing ideologue while elated conservatives swooned over the promotion of a protégé of the late Justice Antonin Scalia.

Five years later, the court’s junior conservative justice has surprised legal advocates on both ends of the spectrum, defying initial expectations, staking out independent ground, and at times conspicuously breaking with the Republican president who put her on the bench.

As the court prepares to hand down its most consequential rulings of the year by the end of June, Barrett is widely viewed as a pivotal vote to watch.

“Justice Barrett has emerged as the center figure, the swing justice, on the current Roberts Court,” said Harvard Law professor and constitutional scholar Noah Feldman, who does not share Barrett’s judicial philosophy but supported her confirmation.

“Justice Barrett is a dyed-in-the-wool conservative who is deeply committed to rule-of-law principles,” said Feldman. “The reason she’s ended up at the center of this court is that the arch-conservatives are so reactionary, so far to the right.”

When the court unanimously blocked Colorado from kicking Trump off the 2024 presidential ballot, Barrett wrote separately to chide her conservative colleagues for a ruling she called unnecessarily broad and to admonish the liberals for issuing a statement she said was strident in tone. “Writings on the Court should turn the national temperature down, not up,” she wrote.

Barrett signed on to the historic opinion that that granted Trump sweeping immunity from criminal charges for his role in the effort to overturn the results of the 2020 election, but broke with the other conservative justices to insist the president could still be prosecuted for some attempts to meddle in the electoral vote.

And, in a high stakes dispute over the nation’s first religious charter school, a long-sought goal among religious conservatives and backed by the White House, Barrett recused herself from the case without explanation. The resulting 4-4 tie among the justices helped give liberal opponents of the school a win.

“She’s not just following the partisan political winds. She’s not just following the latest fashions in judging. She’s following what she thinks of as fundamental principles of legal judgment which she’s gotten from the late Justice Scalia, who was her old mentor,” Feldman said.

To be sure, Barrett has played a key part in dramatic rightward shifts in American law, voting to overrule Roe v. Wade, end affirmative action, limit the power of federal agencies, and expand the rights of gun owners. But she’s also taken positions that her critics have found inconsistent and unprincipled.

When Trump made emergency appeals to the high court earlier this year seeking to override lower court orders, Barrett joined Chief Justice John Roberts and all three liberal justices in narrow 5-4 decisions that denied the president relief.

In January, she voted to reject Trump’s bid to delay sentencing for his New York felony conviction ahead of the inauguration, and later, voted to force the administration to pay out nearly $2 billion in foreign aid money that Trump had wanted frozen.

In a similar but separate case involving Trump’s freeze on federal education grants for state teacher training, Barrett took the president’s side, overriding a district court order that the grants continue.

“She is probably a little bit more moderate, a little more hesitant than other people may have predicted,” said Josh Blackman, a prominent conservative constitutional scholar at South Texas College of Law, who was critical of Barrett’s nomination from the start and now believes she should step down.

MAGA movement loyalists have increasingly lashed out at Barrett, some branding her a “DEI judge” and a “DEI appointee.”

Mike Davis, conservative lawyer and close Trump ally, has repeatedly called Barrett a “rattled law professor with her head up her ass.” Former Fox anchor and commentator Megyn Kelly said she worries Barrett is “a little squishy.”

“Please, Donald Trump, make sure you find a Scalia as our next Supreme Court justice if you get to appoint one,” implored podcaster Glenn Beck in March.

Sources close to Trump have told ABC News that the president has heard the discontent and is frustrated that Barrett and his other high court nominees — Justices Neil Gorsuch and Brett Kavanaugh — have not more aggressively defended his second-term agenda.

“I think she’s brilliant. I think she was an excellent law professor. I don’t know if she is approaching the job with the sort of consistency and sort of backbone that you would want from a Supreme Court justice,” said Blackman.

Going further, some of Barrett’s critics claim the breaks with Trump have become personal, pointing to the justice’s facial expression during an encounter with the president in the House chamber following his joint address to Congress in March. Video of that moment went viral online.

“That look to me was a strange look,” said Patrick Bet-David, a right-wing commentator and host of the PBD podcast. “Maybe we’re reading into it, maybe there’s nothing there. But it was kinda weird how she looked at the president.”

Steve Bannon, Trump’s former chief strategist turned host of the “War Room” podcast, said the look was “about as close to stink eye as you can get. I’ve had a couple of my ex-wives look at me like that.”

Justice Barrett did not respond to ABC News’ request for comment, but her friends and former colleagues say the criticism of her rulings — and facial expressions — is unfair and overblown.

“There’s nothing in her work as a justice that is incongruous with what we knew from her scholarly career, or from the confirmation proceedings,” said Rick Garnett, a close Barrett friend, former neighbor, and Notre Dame law school colleague.

Justice Barrett has most often aligned with fellow Trump appointee Justice Brett Kavanaugh (90% of the time) and least aligned with liberal Justice Sonia Sotomayor (63% of the time) in votes on cases argued before the court, according to data compiled by Adam Feldman, creator and author of Empirical SCOTUS blog.

“There are some people on both sides of the aisle, I suppose, whose understanding of a judge is — a good judge is the one who always gives you what you want,” said Garnett. “That’s not my understanding of a judge, and I don’t think that’s ever been what, you know, most Americans want judges to be.”

Still, many Republicans are haunted by some of the party’s past picks for the high court who later morphed into frequent votes for the left rather than the right. Some have likened Barrett to the late Justice David Souter, who was appointed by Republican President George H.W. Bush and later branded a turncoat.

“There’s really no comparison to be made between [Barrett] and Justice Souter except for the fact that each of them is being consistent to the judicial philosophy they brought to the bench,” said Feldman, a former Souter clerk who worked at the court alongside Barrett when she clerked for Justice Scalia.

Both critics and admirers of Justice Barrett say they see hallmarks of her near-decade experience as a law professor at the University of Notre Dame.

To Blackman, Barrett seeks out a clear theory to justify her position on a given case. “Academics like theories. They want things to be explained where every facet of a case is understood. Barrett wants that from lawyers [arguing a case],” he said.

Garnett, a law professor and former Barrett colleague, said her writings reflect a desire to educate the audience. “I had a chance to observe her as a teacher and a scholar and a faculty member for a long time, and in my view,” he said, “the opinions are extremely well-executed and easy to read, which is not a surprise.”

This September, Barrett will release her first book as a justice, promising to “pull back the curtain on judicial process, as well as on her path to the court,” according to an announcement by publisher Sentinel Books. It will be titled “Listening to the Law: Reflections on the Court and Constitution.”

Barrett has also increasingly used occasional public appearances as an opportunity to cultivate her public image, appearing alongside the court’s senior liberal, Justice Sonia Sotomayor, in an apparent attempt to shore up opinion of the court and promote civility.

“I know that justice Sotomayor respects me and we have affection for one another — I respect her very much — even when we disagree deeply about the merits.” Barrett said last year at a joint event at George Washington University.

As for President Trump, respect for Barrett remains his public position on her tenure, despite any private misgivings, likely because he still needs her vote in the ongoing legal onslaught against his second-term agenda.

“She’s a very good woman. She’s very smart,” Trump said when asked in March about the right-wing attacks on Barrett.

In the coming days, Barrett and the high court will hand down opinions in cases that have significant implications for Trump and his priorities, including a decision on an executive order ending birthright citizenship and three nationwide injunctions issued by district court judges to block it.