Simpson faces a primary challenger from tea partier Bryan Smith, who has managed to collect a number of endorsements from prominent conservative groups including the Club for Growth and FreedomWorks. A week earlier Smith was endorsed by the National Association of Gun Rights PAC.
In his endorsement, Romney highlighted Simpson having voted 40-times to repeal Obamacare as well as his A-plus rating with the National Rifle Association and the fact that Simpson co-sponsored the Balanced Budget Amendment Act.
The race is largely seen as representative between tea party and more mainstream wings of the Republican party. Simpson is often described as a close ally of House Speaker John Boehner (R-OH). Romney himself has notable ties to Simpson, as national political director for Romney's 2012 presidential campaign, Todd Cranney, is working on Simpson's re-election campaign.