Donors to the Republican National Committee gathered this weekend for the first time since Donald Trump’s defeat just down the road from his Mar-a-Lago home — a sign that the institutions of the party remain centered around the former president. The bulk of the RNC’s spring retreat took place a 10-minute drive south of Trump’s club, at Palm Beach’s Four Seasons resort. There, around 360 donors mingled poolside at the beachfront hotel with Republican officials, including chairwoman Ronna McDaniel and co-chair Tommy Hicks. But on Saturday night, guests were shuttled up the road to Mar-a-Lago, where Trump will address the...