Follow the money, and you see a pattern: lobbyists and corporate PACs backing the moderate, and the Club for Growth backing the conservative.

The bloodiest fight between the business lobby and the Club for Growth is in Idaho, where the Club is backing Bryan Smith in a primary challenge to Simpson…

Simpson supports one of the least defensible federal corporate welfare boondoggles — the sugar program, which drives up costs for food makers and consumers while enriching a few sugar growers. Seven different sugar-industry PACs have donated to keep Simpson in office.

The PACs of some of K Street’s most prominent firms also turn up on Simpson’s donor list, including Baker Donelson, DLA Piper, and Dickstein Shapiro. And the U.S. Chamber of Commerce is currently spending $250,000 on ads for Simpson.

The Club for Growth — funded largely by libertarian and conservative business owners — has bundled $300,000 for Smith’s campaign and has spent nearly half a million on ads.