Marvin Nicholson asked his golfing buddy to be a groomsman in his wedding.

That normally would not be a big deal, or even out of the ordinary. But Mr. Nicholson has spent the last eight years as the White House trip director and a personal aide to the president, who happens to be his golfing buddy.

Shortly after President Obama’s star-studded farewell party on Jan. 6 at the White House, he boarded Air Force One with a soon-to-be wedding officiant, Secretary of State John Kerry. They arrived early that morning in Jacksonville, Fla., to take part in the evening wedding of Mr. Nicholson and Helen Pajcic.