Only once has Tarkanian gotten the nomination for federal office, that being last year for Congress, and he lost when there was extensive voter fraud that cost Donald Trump, 2 House seats and the Senate race (not to mention the legislature). As I said to someone else, I expect Steve Bannon did enough research before backing Tarkanian (unlike those who backed Angle for Senate in 2010 when it was clear she couldn’t win a general).
Tark actually is a two-fer for federal office. In 2012, he won the nomination for the newly created NV-4, but lost to Democrat Steven Horsford with 42% to Horsford’s 50%. (Crescent Hardy would later sack Horsford in the 2014 midterm election)