On a muggy October morning in 2007, Miami’s top federal prosecutor, Alexander Acosta, had a breakfast appointment with a former colleague, Washington, D.C., attorney Jay Lefkowitz. It was an unusual meeting for the then-38-year-old prosecutor, a rising Republican star who had served in several White House posts before being named U.S. attorney in Miami by President George W. Bush. Instead of meeting at the prosecutor’s Miami headquarters, the two men — both with professional roots in the prestigious Washington law firm of Kirkland & Ellis — convened at the Marriott in West Palm Beach, about 70 miles away. For Lefkowitz,...