On a sunny June morning eight years ago, Donald J. Trump arrived at his golf resort in Scotland, the day after Britain voted to leave the European Union. At that time, he took credit for predicting Brexit and said it foretold victory in the insurgent presidential campaign he was mounting back home. On Friday, a second-term President Trump returned to that resort, Trump Turnberry, with a good part of what he said in 2016 now a reality. He had correctly claimed that the political forces that drove Brexit went beyond a single country. Five months after that visit, Mr. Trump captured the White House, having played to anxieties about immigration in ways that echoed the “Vote Leave” campaign. Yet in Britain, history has diverged from Mr. Trump’s vision in important respects. Polls show that close to 60 percent of Britons now believe Brexit was a mistake. Prime Minister Keir Starmer has made mending relations with the European Union one of the priorities of his Labour government.