CJR examined the winning percentage of the five biggest outside spending groups in these primaries—defined as the proportion of their expenditures that either supported a winning candidate or opposed a loser. The data shows (click to enlarge) that the Club for Growth and FreedomWorks, the two heavyweight spending groups that back the right wing of the GOP, both did about twice as well picking winners of primaries as they did picking winners of the general election. Again, it may not be surprising that spenders would get better returns on primary bucks—but it’s the same measure that was widely used to pan their performance in the general election. Many of these groups were also distinctive in the degree that they focused on primaries, even as the biggest outside spending groups overall spent upwards of nine out of ten dollars on the general election.

Even the Democratic outside spending group Majority PAC did well in Republican primaries. It devoted most of its GOP primary expenditures to attacking Missouri Senate candidate Jon Brunner, whose defeat paved the way for the nomination of Todd Akin—who promptly thereafter shared his now-infamous views on “legitimate rape.”

The powerful showing by very conservative spending groups in the 2012 primaries influences Congressional Republicans in several ways. As reporters often note, their positions on key votes before Congress are carefully heeded on Capitol Hill. The most dramatic instance of conservative Republicans’ refusal to negotiate with the president, in which the party’s right wing defeated House Speaker John Boehner’s Plan B on fiscal cliff negotiations before it came to a vote, came after leading Tea Party spending groups called for plan’s defeat. More recently, the Club for Growth’s acceptance of a Republican plan to suspend the debt ceiling was portrayed as an important factor in the bill’s passage.

But reporters often stop short of connecting the dots between this lobbying influence and the groups’ heavy spending and strong track record in Republican primaries. Some experts say that the greatest impact from conservative dominance of outside spending may be the fear it generates among Republican incumbents of a primary challenge from the right. “As much as anything it’s the threat of a primary from these groups, ” said Norman Ornstein of the American Enterprise Institute. “It does create a serious challenge to leaders in trying to keep their members in tent on deals that involve compromise.”

The political consequences of this pressure on the right have begun to raise alarms among mainstream Republican groups. The Wall Street Journal reported that after several stinging defeats on Election Day, Republican leadership in the Senate was planning to take a more active role in the party primaries to ensure more electable candidates. Karl Rove’s Crossroads groups, reported The Washington Post, are considering joining the fray as well:

Where until now it battled only in general elections and against Democrats, Crossroads is considering whether to start picking sides in Republican primaries. The idea would be to boost the candidate it deems most electable and avoid nominating the kind of flawed and extreme ones who cost the party what should otherwise have been easy Senate wins in Florida, Missouri and Indiana.
John Feehery, a Republican strategist who managed communications for former House speaker Dennis Hastert and then-Minority Whip Tom DeLay, said he hoped that mainstream groups would get involved in GOP primaries, but that outside money was only one of several factors at play.

“The problem is that it is hard to get moderates to vote in primaries,” Feehery said in an email. “So a more moderate message doesn’t work well. So what ends up happening is that the more moderate groups get forced to out-conservative the conservatives and then it gets real ugly.”

The signals from the Republican establishment that it will take a greater role in party primaries have not been lost on the more hardline groups that currently dominate outside spending. Chris Chocola, the president of the Club for Growth, fired back in a column in the Kansas City Star that charged party leaders with confusing “conservative” with “unelectable”:

In the wake of some missed opportunities to pick up seats in the U.S. Senate over the last few cycles, one tactical change floated by the GOP establishment is that the party apparatus and its affiliated Super PACs should play a more influential role in primaries to make sure that more “electable” candidates are nominated.

It is hard to imagine a bigger mistake.

Sasha Chavkin covers political money and influence for CJR's United States Project, our politics and policy desk. He has written for ProPublica, the Center for Public Integrity, and The New York World. Follow him on Twitter @sashachavkin.