He was a Democrat, and switched to Republican in 2015.
Thanks for the info!
google sez:
Is Eric greitens a Republican or a Democrat?
On September 26, 2015, Greitens officially announced his candidacy for Governor of Missouri as a Republican. ... Democrat-turned-Republican Greitens faced Republican-turned-Democrat Chris Koster in the general election on November 8, 2016, and won with 51.3% of the vote to Koster’s 45.4%.