WASHINGTON — President Biden stunned journalists Thursday by confusing Vice President Kamala Harris and former President Donald Trump — shortly after he confused Vladimir Putin and Volodymyr Zelensky at a different event.

“Look, I wouldn’t have picked Vice President Trump to be vice president if I think she’s not qualified to be president,” the 81-year-old said to gasps and groans from journalists at the annual NATO summit.

Biden spoke with a soft, raspy voice, frequently paused to cough, and at points lost his train of thought at what his aides had promoted as a “big boy press conference” at Washington’s Convention Center— which had been called dispel mounting Democratic calls for him to step aside after a confused June 27 debate against Trump.

Trump, 78, ridiculed his successor in a statement on social media.

“Crooked Joe begins his ‘Big Boy’ Press Conference with, “I wouldn’t have picked Vice President Trump to be vice president, though I think she was not qualified to be president.” Great job, Joe!” the ex-president wrote.

The event, closely watched by Democrats weighing whether to join calls for him to step aside, also included contradictory remarks, forgotten questions and rambling answers that didn’t directly address the question asked.

“I’m catching hell from my wife” because his staff “add things” to his schedule, Biden said at one point after taking the stage nearly two hours late and sticking closely to teleprompters for a seven-and-a-half-minute opening statement.

At one point, Biden denied reports that he told Democratic governors last week that he intended not to do events after 8 p.m. to avoid embarrassing stumbles — saying it was “not true” and that he’s instead trying to “pace” himself better.

“My schedule has been full bore” since the debate, Biden argued.

Fourteen House Democrats and one Democratic senator have called on Biden to relinquish the presidential nomination ahead of the Nov. 5 election — but thus far he has insisted he will press forward and defeat Trump.

Polls show Biden’s support cratering since the debate as fellow Democrats express fear of a Trump landslide.

Democrats who support Biden were anxious about the event at Washington’s Convention Center — the president’s first time formally facing a room full of reporters in Washington since November 2022 and his first extended Q&A session with journalists since his confused June 27 debate performance.

“I feel like the narrative needs to change. So either Dems need to get behind Biden or he needs to step aside. But we are losing time,” a Democratic source close to the White House told The Post before the press conference.