Sen. Richard Lugar's loss in yesterday's Indiana Republican primary — the third such primary loss for a Republican senator since 2010 — was a victory for state treasurer Richard Mourdock and the conservative wing of the Republican Party, which painted the six-term senator as too liberal. But, Lugar's loss may say more about the increasing role of outside money than either of the candidates in the race.

The primary battle was fueled in part by the biggest outside money dump of any congressional race thus far. Leading the money charge was the anti-tax group Club for Growth, which accounted ...