President Biden’s campaign is celebrating what the White House calls his “big boy press conference” tonight at the NATO summit. The hourlong performance leaves Democrats calling for his replacement, playing defense against the bully pulpit and the president’s case that he alone can beat President Trump.

“Do not go gentle into that good night,” the British poet, Dylan Thomas, wrote in 1947. “Old age should burn and rave at close of day. Rage, rage against the dying of the light.” Mr. Biden raged at Trump, Russia, and his Democratic detractors, burning with the heat of a man clinging to the office he craved for half a century.

It was the rebound Mr. Biden needed, not just because of his disastrous debate outing, but because the event started an hour late. The delay left the press with nothing to talk about but Mr. Biden’s stumble earlier at the summit where he introduced President Zelensky of Ukraine as “President Putin” of Russia.

Mr. Biden caught his mistake and corrected it. “I’m so focused on beating Putin,” he explained. Although people often confuse names, with the world hanging on the oldest president in history’s every word, it was a bad omen — and it rolled dozens of times on TV before he ever stepped up to meet the press.

Showing up at last, Mr. Biden was plagued by a cough and, in a jumbled response to the very first question, again transposed names, this time Vice President Harris’s. “I didn’t pick Vice President Trump to be vice president,” he said, “do I think she was not qualified to be president.”

It was almost possible to hear Democrats groaning, “Here we go again.”

Members of the press corps, selected off a prepared list, ignored the stumble until Mr. Biden began to exit, whereupon they shouted questions as a group. The NBC News White House chief correspondent, Peter Alexander, rose above the rest, saying the former president was “using” misnaming Harris “to mock you.”

Asked how he would “combat that criticism” by Trump, Mr. Biden responded, “Listen to him.” He no doubt meant his opponent’s own misstatements, policy positions, and rhetoric. But it came across as a command to heed the Republican’s commands.

Failing to stick that landing, however, will matter little to Mr. Biden’s target audience, which was jittery Democrats more than the electorate at large. After vanquishing his cough, the embattled incumbent performed a highwire act glutted with half a century of policy knowledge to confront concerns about his mental state.

A reporter asked if Mr. Biden would submit to a “cognitive test.” He said he had taken three “neurological exams” during his presidency, “and as recent as February, they say I am in good shape. … You might want to ask Trump for his, okay?”

It was another deft political dodge, ignoring that Trump had taken the Montreal Cognitive Assessment in office and released his score, 30 of 30. Asked if “the limits you have acknowledged” meant he wasn’t “up to” the job, Mr. Biden denied the assessment and reframed his recent troubles.

“It would be smarter for me to pace myself a little more,” Mr. Biden said. He dismissed reports, credited to the White House, that he can only function from 10a.m. to 4p.m. “I love my staff,” he said, “but they add things all the time.”

Near the end of the press conference — having made the case for his policies, foreign and domestic — Mr. Biden twice said, “We’ve got to finish this job.” He argued that inflation is “down,” the border secured, that Trump has an “affinity for authoritarians,” and that he’s hostile to women’s rights.

“Grocery prices have fallen since the start of the year,” Mr. Biden said, choosing a point of reference that fixed the runaway increases on his watch in a positive light. Being able to spin the facts into the best political argument helped in a way it wouldn’t were the nation not questioning his ability to think on his feet.

Mr. Biden also said that he is working toward a “path for peace and stability” in the Israel-Hamas war. As with laying high food prices at the feet of grocery stores, he argued that “the most conservative” cabinet in Israel’s history had opposed any progress, insisting that “there’s no answer other than a two-state solution.”

Acknowledging concerns in his party even as he touted his record to undermine them, Mr. Biden noted how many delegates he’d racked up and votes he’d won in the primaries. “If I show up at the convention,” he said, “and they say they want someone else, that’s the democratic process.”

Mr. Biden then went into his familiar whisper mode. “It’s not gonna happen.” It’s impossible to know if it was an off-the-cuff remark or calculated to soothe those calling for an open convention. Regardless, he is now holding the door open for the nomination at Chicago in August and daring a challenger to walk through it.

It’s clearer than ever that Mr. Biden will not “go gentle into that good night.” At 81, he will “rage and rave at the close of day.” Some Democrats may see light dying in his eyes, but Thursday night the world saw a president who is not yet ready to shrink into the political shadows and surrender the White House without a fight.