In 1984, Nieves enlisted in the United States Navy, serving ten years as a Hospital Corpsman, as a field medic alongside the Marines.
In August 2010, after winning the Senate primary, he pulled a gun on a man who worked for his opponent's campaign.
In the report by Bell, he is said to have been hit with Nieves' spit in the face as well as kicked and punched while lying on the ground shirtless.
[2] Nieves denied any assault had occurred and his campaign manager, who was present during the entire visit by Bell, concurred with this denial.
In 2014, Nieves ran an unsuccessful campaign for the position of Recorder of Deeds in Franklin County, Missouri, losing in the Republican primary.