WASHINGTON

The Supreme Court announced its big campaign finance decision at 10 in the morning last Thursday. By 10:30 a.m., after Justice Anthony M. Kennedy had offered a brisk summary of the majority opinion and Justice John Paul Stevens labored through a 20-minute rebuttal, a sort of twilight had settled over the courtroom.

It seemed the Stevens era was ending.

Justice Stevens, who will turn 90 in April, joined the court in 1975 and is the longest-serving current justice by more than a decade. He has given signals that he intends to retire at the end of this term, and his dissent on Thursday was shot through with disappointment, frustration and uncharacteristic sarcasm.

He seemed weary, and more than once he stumbled over and mispronounced ordinary words in the lawyer’s lexicon  corruption, corporation, allegation. Sometimes he would take a second or third run at the word, sometimes not.

But there was no mistaking his basic message. “The rule announced today  that Congress must treat corporations exactly like human speakers in the political realm  represents a radical change in the law,” he said from the bench. “The court’s decision is at war with the views of generations of Americans.”