The choice follows weeks of intense behind-the-scenes dialog with the Ukrainians, made extra pressing after Russia started a significant assault on Kharkiv round Might 10.

Three days later, on Might 13, Mr. Sullivan, Mr. Austin and the chairman of the Joint Chiefs of Workers, Gen. Charles Q. Brown Jr., held considered one of their often scheduled safe video conferences with their Ukrainian counterparts. As soon as once more, the Ukrainians pressed for Mr. Biden to carry U.S. restrictions on firing into Russian territory, arguing that the president’s considerations about escalation had been overblown. However now, they stated, the difficulty had grow to be extra pressing as a result of the Russians had been shelling civilian websites round Kharkiv from inside their border — understanding that the Ukrainians couldn’t absolutely reply.

After the assembly, officers stated, Mr. Sullivan, Mr. Austin and Common Brown determined to suggest to the president that he reverse his place. However they stored the choice very shut. Two days later, on Might 15, Mr. Sullivan conveyed the advice to Mr. Biden, who — for the primary time — stated he was inclined to carve out an exception that might permit the Ukrainians to strike again, even when Russian assaults had been coming from only a few miles behind the Russian border. By then, Mr. Blinken was already in Kyiv and had heard the case for a reversal instantly from President Volodymyr Zelensky.

The identical day because the non-public assembly with Mr. Sullivan, the president noticed Gen. Christopher G. Cavoli, the four-star commander of the U.S. European Command and the supreme allied commander for Europe. He was in Washington for an annual assembly of all of the combatant commanders, and instructed Mr. Biden that he additionally agreed that the ban on firing into Russia was posing a hazard to Ukraine — although he, too, one official stated, was involved concerning the potential Russian reactions.

Mr. Blinken returned from Kyiv and noticed Mr. Biden and Mr. Sullivan on the night of Might 17 within the Oval Workplace, saying that he emerged satisfied that the US had to alter its stance. It was clear by then that Mr. Biden was in settlement, officers stated, however the president insisted that earlier than he issued a proper resolution, he needed a gathering of his nationwide safety “principals” to contemplate the dangers. That assembly didn’t happen till final week, simply as information of Mr. Blinken’s change of view leaked out.