Inside the White House, a Gun Industry Lobbyist Delivers for His Former Patrons

In an interview, Mr. Keane praised Mr. Williams, saying “he understands the product, obviously, having worked at the American Suppressor Association.” That association said it was “thrilled” with the ban’s end; the group also dismissed safety concerns, noting that the sales would be regulated by the State Department and that foreign-made silencers were already available for purchase in other countries.

But some in military, diplomatic and arms control circles defended the ban and expressed alarm about its lifting, which was announced on Friday afternoon in a little-noticed posting on the website of the State Department’s Directorate of Defense Trade Controls. Although the department’s rules had long permitted selling silencers to foreign governments, they did not allow sales to private companies or individuals, whose use of the devices is more difficult to monitor.

Lincoln P. Bloomfield Jr., who was assistant secretary of state for political-military affairs when the ban was enacted in 2002, said the policy was intended to prevent American equipment from making its way to hostile groups that might use it against American service members, especially during the Afghanistan and Iraq wars.

“Terrorist groups were using garage door openers to blow up U.S. troops; you kind of think twice about what you are exporting,” said Mr. Bloomfield, who added that such dangers still exist today. “Who are you selling these silencers to?” he said. “I sure hope that none of these are aimed at U.S. or allied forces.”

A State Department spokeswoman said the policy change was made to benefit American manufacturers. “U.S. companies should have the same opportunity to compete in the international marketplace as other manufacturers around the world,” the spokeswoman said. She also said that silencers were more readily available in foreign countries now than when the ban was imposed.

The White House did not respond to a request for comment. Mr. Williams declined to comment.

An examination of Mr. Williams’s rise from trade group advocate to West Wing lawyer reveals that White House tumult and turnover created opportunities for him.

After joining Mr. Trump’s campaign in 2016, Mr. Williams, at age 30, became an assistant deputy general counsel at the Office of Management and Budget, then led by Mick Mulvaney.