In late June 2017, Petersen filed an
exploratory committee to consider running for the U.S. Senate seat in Missouri. On July 4, 2017, Petersen formally announced his bid for the Republican nomination in the
2018 Missouri Senate race. In September 2017, Petersen was banned from
Facebook during his senate campaign for giving away an
AR-15 style rifle as a promotion and criticizing his
Democratic opponent
Claire McCaskill's positions on
gun rights. The ban was lifted after
Fox News reported that Facebook's COO
Sheryl Sandberg had made max donations to McCaskill's campaign. The raffle drew renewed controversy in February 2018 when the
school shooting in Parkland, Florida caused the
Springfield News-Leader to investigate.
KMOV in
St. Louis scrutinized Petersen over his views on gun control in light of the shooting. Petersen also reportedly received the national record for the largest
Bitcoin donation in American campaign history. Fox News reported in January 2018 that Petersen was one of two "potential general election challengers" in the election. Petersen officially filed with the
Missouri Secretary of State for the US Senate seat as a Republican on February 28, 2018. On March 6, Petersen announced a new AR-15 raffle on Facebook. His personal page was banned after the livestream was recorded. In July he announced a raffle for a machine, similar to a 3-D printer, that can produce "untraceable gun parts". His campaign said 3-D printing technology has been described as the "end of gun control". In the runup to the Republican primary election in August, President
Donald Trump endorsed Petersen's rival
Josh Hawley and campaigned for him. Petersen expressed displeasure about Trump's involvement in the primary. In the August 7 primary Petersen came in third with 8.3% of the vote. ==Political positions==