WASHINGTON (Reuters) - Brett Kavanaugh spent a collegial first day on the bench as a U.S. Supreme Court justice on Tuesday that contrasted sharply with the venom of his confirmation process, taking an active role in arguments alongside his eight new colleagues.

Kavanaugh, a veteran of such proceedings after 12 years on an influential U.S. appeals court, looked at ease as he asked several questions during two hours of lively oral arguments involving a federal sentencing law for repeat offenders.

It seemed like business as usual in the ornate courtroom, three days after Kavanaugh was confirmed by the Republican-led Senate despite being accused of sexual assault by a university professor named Christine Blasey Ford. Appointed by President Donald Trump, Kavanaugh’s confirmation cemented a conservative majority on the court that could last for years.

Kavanaugh took his seat at the right end of the courtroom’s mahogany bench - the location assigned to the court’s junior-most member - and wore traditional black robes like the other justices. Retired Justice Anthony Kennedy, the 82-year-old jurist who Kavanaugh replaced, was in the courtroom, as were members of the new justice’s family.

With police standing by, a small group of protesters demonstrated outside the courthouse, holding signs saying “Shame” and “He sits on a throne of lies,” while chanting, “This isn’t over, we’re still here.” With courtroom security tight, there were no disruptions by protesters during the arguments, as there had been during Kavanaugh’s confirmation hearings.

Chief Justice John Roberts formally welcomed Kavanaugh, 53, to a court that now has five conservative members and four liberals.

“We wish you a long and happy career in our common calling,” Roberts told Kavanaugh, who could serve for decades in the lifetime job.

The bitterly divided Senate voted 50-48 on Saturday to confirm Kavanaugh, with just one Democrat supporting him. Kavanaugh’s confirmation gave the Republican president a political victory ahead of crucial Nov. 6 congressional elections.

Kavanaugh was Trump’s second selection for the nation’s highest judicial body, following conservative Justice Neil Gorsuch last year.

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Kavanaugh posed questions to lawyers in both cases before the court, his first one coming about 20 minutes into the arguments.

At one point, Kavanaugh could be seen having a lighthearted exchange with liberal Justice Elena Kagan, seated next to him. At another point, liberal Justice Sonia Sotomayor appeared to pinch Gorsuch, sitting next to her, to playfully illustrate her point about what constitutes a violent act. Gorsuch responded with a faux grimace of pain.

Tuesday’s cases involved the 1984 Armed Career Criminal Act, a “three-strikes-and-you’re-out” criminal sentencing law that boosts prison sentences for people who are convicted of crimes involving guns if they previously have been convicted of certain other crimes.

The cases, involving a Florida robbery and burglaries in Tennessee and Arkansas, challenged the types of crimes that qualify as violent felonies under that law and can lead to 15-year mandatory minimum sentences.

Roberts prompted laughter when he described asking his law clerks to try to grab a dollar bill from his hand to determine if that constituted a violent act.

“I’m not saying nobody could do it ... but it requires a lot of force, more than you might think,” Roberts said.

Based on Tuesday’s arguments, defendants could win in both cases, with liberal justices likely to be joined by some conservatives in the majority. Kavanaugh appeared less sympathetic to the defendants than Gorsuch.

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ENVIRONMENTAL CASE

Kavanaugh had served as a judge on the U.S. Court of Appeals in Washington since 2006.

Before Tuesday’s arguments, the justices turned aside appeals of a 2017 ruling authored by Kavanaugh while on the lower court striking down a 2015 environmental rule imposed under Democratic former President Barack Obama regulating a potent greenhouse gas linked to climate change.

The justices privately made the decision to reject the appeals by an environmental group and companies that supported the regulation before Kavanaugh’s confirmation, and announced the action on Tuesday.

Kavanaugh is expected to push the court further to the right as he is replacing Kennedy, a conservative who sometimes voted with the liberal justices on key social issues such as abortion and gay rights.

His nomination had appeared safe until Ford last month went public with allegations that Kavanaugh sexually assaulted her in 1982 when they were high school students in Maryland. Two other women accused Kavanaugh of sexual misconduct dating to the 1980s.

Kavanaugh denied the allegations and during a Senate hearing accused Democrats of an “orchestrated political hit.”

He later expressed regret over some of his comments. But critics said Kavanaugh’s demeanor raised questions about his temperament and potential political bias in deciding cases.

At a White House ceremony on Monday night, Kavanaugh said he was starting his new job with “no bitterness,” seeking to be “a force for stability and unity.”

Trump on Twitter on Tuesday said he was “very proud” of Kavanaugh and his family, and disparaged the anti-Kavanaugh protesters.