MIAMI — One day in the State Capitol in Tallahassee, Marco Rubio, the young speaker of the House, strayed from the legislative proceedings to single out a lanky, silver-haired man seated in the balcony: a billionaire auto dealer named Norman Braman. This man, Mr. Rubio said in effusive remarks in 2008, was no ordinary billionaire, hoarding his cash or using it to pursue selfish passions. “He’s used it,” Mr. Rubio said, “to enrich the lives of so many people whose names you will never know.” As it turned out, one of the people enriched was Mr. Rubio himself. As Mr....