Democratic candidate Betsy Markey, a Fort Collins resident, is turning Colorado’s Fourth Congressional District a light shade of blue, according to the most recent House ratings from the Rothenberg Political Report.

With two of the most populous cities in the district (Fort Collins and Loveland), Larimer is a top swing county in our desirable swing state. But Markey’s gains there aren’t necessarily good news for the Obama campaign.

In 2004, John Kerry lost the county to George W. Bush despite the fact that Democrat Ken Salazar bested Republican Pete Coors for Senate by nearly the same percentage points. And Markey, then Larimer’s Democratic County Party Chair, was instrumental in creating the Salazar team’s winning Larimer playbook, with little to no assistance or collaboration from Senator Kerry’s coordinated campaign staff. (Disclosure: I worked field operations for the Kerry team for a short time before returning to journalism.) Markey then went on to staff Salazar’s regional field office in downtown Fort Collins.

CD4 has remained solidly red since 1972, with such stealthily conservative alumni as Senator Wayne Allard, former C.U. president Hank Brown, and Senate candidate Bob Schaffer representing. The Dems’ last attempt to take the district, with former Fort Collins State Representative Angie Paccione, in 2006, was partially foiled by the threatening third-party candidate that Colorado political candidates are so susceptible to, yet too often underestimate.

In the case of 2006, Reform Party candidate Eric Eidsness swept in for a little over 11 percent of the vote. Just after the election, contributor Joshua Zaffos reported on the Eidsness factor for the Rocky Mountain Chronicle:

The numbers from Weld and the northeastern Plains make it difficult to blame Eidsness for Paccione’s failure to win votes there; he appears to have lured supporters from both sides. Without taking too much credit away from Eidsness, who appealed to rural conservatives and urban liberals alike, observers believe many of his votes were protests against the major parties and their attack-ad tactics.

“There was so much negative campaigning between Musgrave and Paccione that some voters got disgusted and went to the third-party candidate, and that’s not uncommon,” says Bill Chaloupka, chair of the political science department at Colorado State University.

Democratic field organizers agree that the flurry of attack ads by both major-party candidates backfired among rural voters who turned to Eidsness, adds [Colorado Democratic Party Chair Pat] Waak.

Words of caution, indeed, for both candidates this election year, as attack ads are inflaming the CD4 race once again. (Read the fifth entry, “The Bitter Battle for the Fourth,” in today’s edition of Panorama, 5280’s daily newsletter, for more on the most recent exchanges between Musgrave and Markey.)