The voters who do turn out in Republican Senate primaries are likely to be highly informed consumers of conservative-friendly news media outlets such as talk radio, prime-time shows on Fox News and conservative magazines and blogs. They may also weigh the endorsements of prominent conservative politicians and organizations. An insurgent candidate who is presented in a favorable light in these outlets may have plenty of ability to reach her target voters, even if she is spending little or nothing on paid advertisements and outreach efforts.

Mr. Rove’s efforts could backfire, therefore, if they result in the insurgent candidate receiving more sympathetic treatment through these channels; the amount of so-called “earned media” that the insurgent receives could outweigh the extra advertisements that the establishment candidate is able to afford.

A related problem is that the insurgent candidates could seek to raise money directly in response to moves by Conservative Victory Project, as Mr. King of Iowa is attempting to do. This could be the case especially when insurgent candidates were otherwise having trouble raising funds.