Trump Backs Away From Deal to Let Ukraine Build Patriot Missiles

President Trump backtracked on Friday from a promise earlier this month to let Ukraine make Patriot missiles, weapons that were sorely needed as a defense interceptor against Russia’s deadly ballistic missile attacks.

On July 8, Mr. Trump had unexpectedly assented to sharing technology behind the missiles to allow Ukraine to build them, saying that “we’ll give them the right to make Patriots” during a meeting with President Volodymyr Zelensky of Ukraine on the sidelines of the NATO summit meeting in Ankara, Turkey. He added: “We’ll show them how to do it.”

When asked about the agreement during a meeting with his cabinet on Friday, Mr. Trump said “we have not agreed to that,” suggesting that he had changed his mind because “it is a hard thing to give away that kind of technology” and because of the risk that “those people you give the technology, they could someday turn on you.”

“You look at war, it has happened a couple of times over the years,” Mr. Trump said. “So we have to be very careful. We guard that.”

Some of America’s adversaries were indeed once allies, wielding weapons that the United States sold to them in friendlier times. In the opening days of Mr. Trump’s war with Iran, for example, Israeli airstrikes appeared to destroy some of the last American-built F-14 fighter jets still in active service, which the United States had sold to Iran during the autocratic regime of the Shah that fell in the Iranian revolution in 1979.

An agreement to allow Ukraine to build the Patriot missiles would require the U.S. government to share its defense technology and for the defense firms that build the systems, including Raytheon and Lockheed Martin, to work with the Ukrainians to manufacture the weapons. Such a project could take months or years, and any defense facility Ukraine builds to manufacture its own Patriots would quickly become a target of Moscow.

Mr. Trump, who held a closed-door meeting with Mr. Zelensky earlier this week, told The Financial Times on Thursday that he was “not sure” about allowing Kyiv to move forward with plans to license the weapons. Mr. Zelensky, for his part, said that he and Mr. Trump “discussed licenses for Patriot interceptor production and several other ideas that could help.”

Continuing a mercurial pattern on the war in Ukraine — sometimes supportive of Ukraine’s war effort, and other times sympathetic to the position of President Vladimir V. Putin of Russia — Mr. Trump appeared on Friday to criticize President Joseph R. Biden Jr.’s efforts to arm Ukraine, even as he acknowledged that he himself had given weapons to the country.

“President Biden, unfortunately, gave a lot away to Ukraine,” Mr. Trump said. “And he gave — so did I. I mean, I gave them the Javelins, the tank-busters. Without the Javelins, that war would have been a one-day war.”

“We have the greatest weapons in the world,” he added. “You have to be very careful about giving out the secrets to those weapons.”

Katie Rogers contributed reporting.