The results of the investigation the F.B.I. is undertaking into the sexual assault allegations against Judge Brett M. Kavanaugh may objectively disqualify or vindicate President Trump’s nominee to the Supreme Court. Regardless, the Senate Judiciary Committee’s extraordinary hearing on Thursday has already uncovered vital evidence about his suitability for the bench: the injudicious temperament he displayed. The eruption of Mount Kavanaugh raises questions about judicial temperament that may be enough on their own to resolve the nomination.

Mr. Kavanaugh fulminated: The process was “a national disgrace.” He interrupted. “What do you like to drink?” he demanded of Senator Sheldon Whitehouse, Democrat of Rhode Island. He invoked old political disputes and argued that the accusations against him were fueled by “pent-up anger about President Trump and the 2016 election” and “revenge on behalf of the Clintons.” He appeared to level fresh political threats: “And as we all know, in the United States political system of the early 2000s, what goes around comes around.”

These qualities endeared him to President Trump, at least for a while. Judge Kavanaugh’s performance “showed America exactly why I nominated him,” the president tweeted. Retribution and distemper — even under extraordinary stress, which can obscure but also amplify a person’s character — are not qualities one should seek in a Supreme Court justice or a judge of any kind. Judge Kavanaugh was not calling balls and strikes. He was swinging wildly at the ball.

This is not about whether an originalist should replace Justice Anthony Kennedy. One almost certainly will. President Trump has confined himself to a list of them, and Senate Republicans have months left to confirm one, at the very least. It is about whether that justice will have both the ability and, crucially, the credibility to render neutral judgments of law. This is also true for the court as a whole, especially in an environment in which groups of justices in both wings of the institution are perceived as political factions that deliver for the parties by which they were nominated.