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Mr. Cardenas later confronted Mr. Castro directly, shouting “asesino” — Spanish for “assassin” — at the Cuban strongman as he passed by. Mr. Castro’s security detail confronted Mr. Cardenas, but were stopped short when he flashed his U.S. delegation credentials at them.

Mr. Cardenas was an employer of — and has been a friend and mentor to — Mr. Rubio, a fellow Cuban-American.

Mr. Cardenas and his wife of 32 years, Diane, have five children.