Donald Trump, speaking at a triumphalist White House ceremony, has made the baseless claim that the new supreme court justice Brett Kavanaugh was “proven innocent” of allegations of sexual assault.

In what he acknowledged was a break from tradition, the US president told a packed East Room on Monday: “On behalf of our nation, I want to apologize to Brett and the entire Kavanaugh family for the terrible pain and suffering you have been forced to endure. Those who step forward to serve our country deserve a fair and dignified evaluation, not a campaign of political and personal destruction based on lies and deception.”

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Trump, often criticised for rubbing salt in national wounds rather than healing them, continued: “What happened to the Kavanaugh family violates every notion of fairness, decency and due process. Our country, a man or woman must always be presumed innocent unless and until proven guilty.”

Clarence Thomas, who was confirmed to the court in 1991 despite sexual harassment allegations by Anita Hill, joined applause in the room. Sitting beside him, Ruth Bader Ginsburg, a liberal justice, did not. All eight sitting supreme court justices were present.

The president added: “And with that, I must state that you, sir, under historic scrutiny, were proven innocent. Thank you. You were.” He turned to shake the hand of Kavanaugh, who said, “Thank you,” as the room erupted in applause again.

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The judge was found neither guilty nor innocent of allegations brought by research psychologist Dr Christine Blasey Ford that, when he was 17 and she 15 in the 1980s, Kavanaugh pinned her to a bed, groped her and tried to remove her clothes while putting his hand over her mouth to stop her screams.

Kavanaugh’s furious, politically charged denials before the Senate judiciary committee raised questions over his judicial temperament and independence. Thousands of protesters staged noisy sit-ins on Capitol Hill as the confirmation process exposed bitter divisions in the Senate and the nation. He eventually secured a place on America’s highest bench on Saturday in a narrow vote almost entirely along party lines. Democrats denounced it as a betrayal of women.

The ranting, tearful Kavanaugh was not in evidence on Monday, though his air of self-assurance and self-destiny was. Early in his remarks, he praised Trump’s “deep appreciation for the vital role of the American judiciary” and thanked him for his “steadfast” and “unwavering” support. “Mr President, thank you for everything.”

Accompanied by his wife, two daughters and parents, Kavanaugh went on to strike a more conciliatory tone, doubtless eager to put the rancour and recriminations of the past month behind him.

Facebook Twitter Pinterest Most supreme court justices applaud during Brett Kavanaugh’s swearing-in ceremony on Monday. Photograph: UPI/Barcroft Images

“The supreme court is an institution of law,” he said, as his new colleagues looked on. “It is not a partisan or political institution. The justices do not sit on opposite sides of an aisle. We do not caucus in separate rooms. The supreme court is a team of nine, and I will always be a team player on the team of nine.”

Kavanaugh carefully said he had worked hard to “promote the advancement of women”, inspired by his mother, a “trailblazer for women”. He pointed out that most of his law clerks in his career have been women, and that he had hired four female law clerks in his new role, “a first in the history of the supreme court”.

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The newly anointed justice added: “The Senate confirmation process was contentious and emotional. That process is over. My focus now is to be the best justice I can be. I take this office with gratitude and no bitterness. On the supreme court, I will seek to be a force for stability and unity. My goal is to be a great justice for all Americans and for all of America. I will work very hard to achieve that goal.”

Activists have warned that Kavanaugh will tilt the court in a conservative direction for decades. He insisted: “I was not appointed to serve one party or one interest, but to serve one nation.” He promised to hear every case with “an open mind”, adding: “Every American can be assured that I’ll be an independent and impartial justice, devoted to equal justice under law.”

Although Kavanaugh was officially sworn in at a private ceremony on Saturday, the event provided an opportunity for Trump and Republicans to take a victory lap on primetime television. The president encouraged the Senate majority leader, Mitch McConnell, to rise; McConnell did so and gave a thumbs up amid a standing ovation. Trump quipped: “I think that’s the biggest hand he ever received.”

Kavanaugh was symbolically sworn in by the retired Justice Anthony Kennedy, whom he replaces. Leading conservative personalities such as Laura Ingraham, David Bossie and Matt Schlapp were also present amid the crystal chandeliers and gold curtains of the East Room.

The first lady, Melania Trump, was absent, however. Her spokeswoman, Stephanie Grisham, said: “The first lady regrets that she will not be able to celebrate with the Kavanaugh family on such a special evening, but she has a longstanding prior commitment she was unable to change at the last minute.”

Laurence Tribe‏, a constitutional law professor at Harvard University, tweeted: “I pity the Justices who had no realistic option but to attend and serve as props for the partisan display. Only Thomas, clapping with gusto, looked like he was really pleased to be there. The others looked like polite hostages. A grim and tasteless spectacle.”

Earlier in the day, Trump had claimed that Kavanaugh was “caught up in a hoax that was set up by the Democrats”. Again he offered no evidence.