Mr. Macron acknowledged that the deal had not addressed crucial concerns, including future nuclear activities in Iran, the use of ballistic missiles and the country’s destabilizing activities in the region. “But we should not abandon it without having something substantial, and more substantial, instead,” he added. “What we decided, together with your president, is that we can work on a more comprehensive deal addressing all these concerns.”

Later, in a news conference before wrapping up his three-day visit to the United States — the first formal state visit of the Trump era — Mr. Macron told reporters that while he could not be certain, he expected that Mr. Trump would disregard his entreaties and withdraw from the nuclear deal after all, given that scrapping it was a campaign promise.

On Capitol Hill, Mr. Macron was greeted warmly with a three-minute standing ovation, and he drew several more ovations throughout his speech as he outlined his vision of global affairs and the alliance between the United States and France, in nearly flawless English.

He opened with a humorous nod to the much-discussed embraces he and Mr. Trump shared at the White House on Tuesday, comparing their interactions to those between the French philosopher Voltaire and Benjamin Franklin when they met in Paris in 1778.

“They embraced each other by hugging one another in their arms, and kissing each other’s cheeks,” Mr. Macron said, pausing for effect. “It can remind you of something.”