Rep. Mike SimpsonMIchael (Mike) Keith SimpsonKey conservative presses for shield law after seizure of NYT reporter’s records Unending Pruitt controversies leave Republicans frustrated The Hill's Morning Report — Sponsored by PhRMA — Tensions mount for House Republicans MORE (R-Idaho), facing a tough primary fight from a Tea-Party-backed candidate, has been endorsed by the Chamber of Commerce.

The Chamber is likely to spend significant money to defend Simpson against attorney Bryan Smith’s (R) challenge. The group has indicated this cycle it’s planning to get more actively engaged in Republican primaries to beat back challenges from conservative candidates.

Their primary has become a proxy battle for the broader civil war war between the establishment and conservative wings of the GOP. Simpson is a close ally of House Speaker John Boehner (R-Ohio), who has fundraised for him.

Simpson has long been attacked in his state for not being conservative enough and has faced primary challenges in the past, but none have been very well-funded.

This time around, however, Smith has the support of the deep-pocketed Club for Growth, a conservative group known to invest millions in races to sway the outcome.

The Chamber of Commerce will help counter any attacks from the Club.