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 demeanor 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 on Thursday, responding to accusations of sexual misconduct at a hearing of the same Senate committee, sent a different message. Judge Kavanaugh was angry and emotional, embracing the language of slashing partisanship. His demeanor 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 is confirmed.

“This whole two-week effort has been a calculated and orchestrated political hit,” he said, “fueled with apparent pent-up anger about 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, Judge 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 Ms. Klobuchar.