WASHINGTON—In the first round of his Supreme Court confirmation hearings early this month, Judge Brett M. Kavanaugh kept his cool under hostile questioning, stressed his independence, and exhibited the calm judicial demeanour that characterized his dozen years on a prestigious appeals court bench.

“The Supreme Court,” he said, “must never be viewed as a partisan institution.”

His performance Thursday, responding to accusations of sexual misconduct at a hearing of the same Senate committee, sent a different message. Kavanaugh was angry and emotional, embracing the language of slashing partisanship. His demeanour raised questions about his neutrality and temperament and whether the already fragile reputation of the Supreme Court as an institution devoted to law rather than politics would be threatened if he was confirmed.

“This whole two-week effort has been a calculated and orchestrated political hit,” he said, “fuelled with apparent pent-up anger about U.S. President Trump and the 2016 election, fear that has been unfairly stoked about my judicial record, revenge on behalf of the Clintons and millions of dollars in money from outside left-wing opposition groups.”

In a sharp break with decorum, Kavanaugh responded to questions about his drinking from two Democratic senators — Amy Klobuchar of Minnesota and Sheldon Whitehouse of Rhode Island — with questions of his own about theirs. He later apologized to Klobuchar.

The charged language recalled Kavanaugh’s years as a partisan Republican, working for Ken Starr, the independent counsel who investigated a series of scandals involving Bill and Hillary Clinton, and serving as an aide in the administration of George W. Bush. It was less consistent with the detached judicial temperament that lawyers associate with an ideal judge.

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All of this, said Judith Resnik, a law professor at Yale, was “partisan and not judicious.” Kavanaugh’s confirmation in the wake of his performance, she added, could leave the Supreme Court “under a cloud of politics and scandal from which it would not recover for decades.”

But his confirmation, which had once seemed all but assured, faced another dramatic turn Friday when Sen. Jeff Flake of Arizona called for a one-week delay of the full Senate’s vote on his nomination to allow for an investigation by the FBI into the allegations against him by Christine Blasey Ford and other women.

Ideology has long figured in the Supreme Court’s work, but a sharp partisan split on the court is a recent phenomenon. Starting in 2010, the court became divided along party lines, with all five Republican appointees to the right of all four Democratic ones.

Confirmation fights reflect this new reality. The court’s two senior liberals, Justices Ruth Bader Ginsburg and Stephen G. Breyer, were confirmed with just a dozen negative votes between them. More recent nominees have faced furious opposition.

Chief Justice John G. Roberts Jr., a devoted custodian of the court’s prestige and authority, has bemoaned the damage that even ordinary confirmation hearings do to his institution.

“When you have a sharply political, divisive hearing process, it increases the danger that whoever comes out of it will be viewed in those terms,” he said in 2016. “If the Democrats and Republicans have been fighting so fiercely about whether you’re going to be confirmed, it’s natural for some member of the public to think, well, you must be identified in a particular way as a result of that process.”

Roberts spoke in the wake of a series of confirmation hearings tinged with partisanship but nothing like the all-out war the American public saw Thursday. If the chief justice feared that the court’s reputation could be damaged by them, he has reason to be terrified now.

“We don’t work as Democrats or Republicans,” he said in the 2016 remarks, “and I think it’s a very unfortunate impression the public might get from the confirmation process.”

As it happens, a reliable way to predict how justices will vote in highly charged cases is to check the political party of the president who appointed them. There was one exception to that rule in recent decades: Justice Anthony M. Kennedy could be unpredictable.

Kennedy was nominated in 1987 by U.S. President Ronald Reagan after his first pick, Judge Robert H. Bork, was rejected by the Senate. Many scholars trace the divisiveness of contemporary Supreme Court nominations to the resentments that began with Bork’s confirmation hearings.

Kennedy replaced Justice Lewis F. Powell Jr., who also occupied a seat at the court’s ideological centre. But if Kavanaugh replaces Kennedy, there is little question that he will move the court to the right.

A confirmation hearing is not a courtroom, of course, but experts in law and psychology said there was reason to fear that Kavanaugh’s searing reaction to the recent accusations could affect his work should he be confirmed to the Supreme Court.

“Every bit of research ever done on the subject concludes that judges are human beings with emotional reactions that influence how they decide cases,” said Jeffrey J. Rachlinski, a law professor at Cornell.

“This process clearly has ignited a passionate reaction in Judge Kavanaugh that will doubtless influence him for the rest of his life,” Rachlinski said. “Research on how emotions influence judges suggests that he will be unable to set this experience aside when deciding cases involving relevant subjects or parties who are closely aligned with those he has today treated as personal enemies.”

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Eric J. Segall, a law professor at Georgia State, said Thursday’s hearing both illuminated Kavanaugh’s political outlook and was likely to affect his voting on the Supreme Court if the Senate confirms him.

“His time in the executive branch and his work for Starr suggested he was one of the most partisan nominees in a long time,” Segall said.

“I would think that any person, even acting in totally good faith, would not be able to put aside the obvious trauma of this hearing for him, whether he’s telling the truth, lying or suffering from cognitive dissonance,” Segall said. “This kind of event could greatly affect one’s decision-making in the grey areas that most Supreme Court cases present.”

Michael C. Dorf, a law professor at Cornell, said a Justice Kavanaugh would not consciously alter his approach to his work. “He wouldn’t allow himself to think that he is the sort of person who is voting out of spite,” Dorf said. “But it’s hard to imagine that it doesn’t affect him in much the way that one can imagine that Justice Thomas’ lingering anger affects him.”

In 1991, in a hearing with distinct echoes of the one Thursday, Judge Clarence Thomas vehemently and categorically denied accusations that he had sexually harassed a subordinate, Anita Hill.

He was in the bathtub when he learned that the Senate had confirmed him by a 52-48 vote. “Whoop-dee-damn-doo,” he said, according to his memoir. His reputation had been destroyed, he wrote. “Mere confirmation, even to the Supreme Court,” he wrote, “seemed pitifully small compensation for what had been done to me.”

A bitter Thomas went on to become the most conservative member of the Supreme Court in modern history.

Justice Samuel A. Alito Jr.’s confirmation hearings in 2006 were far less bruising than the ones endured by Thomas and Kavanaugh. But they were painful enough that Alito has said he avoids walking by the Senate building where his hearings were held.

Alito, too, has forged a consistently conservative voting record. And in 2010, he mouthed the words “not true” at a State of the Union address in which President Barack Obama criticized the Supreme Court’s decision in the Citizens United campaign finance case. That overt clash, with a Democratic president on one side and a Republican appointee on the other, was another sign of a deepening partisan divide.

On Thursday, Kavanaugh made plain how devastating the accusations against him were and whom he blamed: Democratic senators. He described the pleasure he had taken in teaching law at Harvard, where he was a highly regarded visiting professor hired by Justice Elena Kagan when she was the law school’s dean.

“Thanks to what some of you on this side of the committee unleashed,” Kavanaugh said Thursday, looking at the Democrats, “I may never be able to teach again.”

It is not easy to trace precisely how the confirmation process affects a justice’s work, Dorf said.

“I don’t think Justice Thomas is consumed by anger,” Dorf said. “But it’s there, and it comes out from time to time.”

Kavanaugh, too, if he joins the Supreme Court, might occasionally employ an extra measure of skepticism in considering arguments in favour of congressional power or put forward by a future Democratic administration, Dorf said.

“It will be impossible to demonstrate a straight line in any given case,” he said, “but I think it’s got to affect him.”