Yesterday, Andrew Romanoff, the former Colorado House Speaker challenging Michael Bennet for the Senate, won the Colorado caucuses, a nonbinding straw poll leading up to the Aug. 10 primaries, which is seen as a key indicator of organizational might. The favored Republican candidate, former Lt. Governor Jane Norton, ALSO lost, to the unheralded tea party favorite Ken Buck.

Romanoff, given his experience in Colorado politics (and the lack of experience on the part of the appointed Bennet), was actually favored in the caucus. But between the results and Bennet’s new ad, touting his reform efforts and positioning himself outside of “broken” Washington, you can see that anti-incumbency will define the 2010 election far more than ant-liberal or anti-conservative sentiment, or even sentiment on particular issues (the most recent poll on the health care bill shows that voting yes would cause 1/3 of the electorate to be more likely to vote for their Congressman, 1/3 to be less likely, and 1/3 with no opinion).

This, more than anything, is why you’re seeing the rise of primaries as we near the election. Some of them are related to health care; in South Dakota, Obama deputy campaign manager Steve Hildebrand has threatened to challenge Stephanie Herseth-Sandlin if she votes against the health care bill. Al Lawson is openly using health care as a way to pressure Allen Boyd in his primary race. SEIU has threatened a primary for Mike McMahon in New York. And Connie Saltonstall, challenging Bart Stupak in Michigan over his hijacking of the health care debate, has attracted the support of Blue America, and DFA is considering jumping in as well. And there’s Bill Halter in Arkansas. Locally, we have Marcy Winograd challenging Jane Harman in CA-36. Up and down the line, voters angry with Washington policies will have the choice to pick someone outside of Congress to represent them.

Ultimately, that’s a healthy development. Primaries create engagement and can effectively check Congressional power. The system was designed for turnover if the people willed it, not lifetime holds on positions of authority.

Primary challenges are difficult and mostly unsuccessful. But this year, something does seem different.