John L Lewis of the United Mine Workers was probably the last union leader actually elected by the membership. For the most part national union officials are elected by delegates appointed by the leadership. Most have never worked a day in the occupations they purport to represent. The teamsters have often been an outlier, endorsing Nixon in 1972, and Reagan in 1980. They have also elected dissidents to leadership positions on occasions. Not surprised to see the rank and file supporting Trump.