This outspoken supporter of President Trump from South Florida was charged on Friday with sending explosive packages to at least a dozen of the president’s critics, apparently bringing to a close an attempted bombing spree that has gripped the country just ahead of the midterm elections.

The suspect, Cesar Altieri Sayoc Jr., 56, was arrested outside a car-repair shop in the Miami area after a fast-moving investigation in which the authorities said they were able to pull a fingerprint from one of the bomb packages and collect Mr. Sayoc’s DNA from two others.