WASHINGTON — President-elect Donald J. Trump on Thursday chose Woody Johnson, the owner of the New York Jets football franchise and one of Mr. Trump’s oldest friends, as his ambassador to Britain. It is just the fourth ambassadorial pick Mr. Trump has announced.
Mr. Johnson’s appointment to the Court of St. James’s, as it is formally known, is a plum assignment. It is usually given to wealthy donors who use the ambassador’s palatial home to become part of London’s high-end social scene.
But the job could be unusually challenging during Mr. Trump’s administration, as Prime Minister Theresa May pushes Britain to leave the European Union and tries to reach a quick trade agreement with the United States.
Mr. Trump supports Britain’s exit from the European Union but has made clear that trade deals, which often take years to negotiate, must favor the United States.
Mr. Johnson, heir to a pharmaceutical and shampoo fortune, has long…