Opinions vary on the viability of Colorado Republican nominee Ken Buck in his challenge to Sen. Michael Bennet. After defeating former Republican frontrunner Jane Norton in the primary, Buck has an even tougher challenge against the incumbent Democrat.

But regardless of whether he claims the seat, simply having Buck’s name on the ballot is expected to be a big help to other Republican candidates in northern Colorado, where he’s popular and well-known as Weld County district attorney.

One of the candidates who could feel the down-ballot breeze is Cory Gardner, whom Republicans in Washington are counting on to take back the 4th district from freshman Democratic Rep. Betsy Markey.

“Having a northern Colorado favorite son head the Republican ticket has to help other GOP candidates in this part of the state, starting with Cory Gardner,” said Eric Sondermann, a Colorado-based independent political consultant. “If the Markey-Gardner contest ends up being a 5-point race, this won’t be a consideration. But if it ends up as a neck-and-neck deal, then every little bit matters when it comes to boosting Republican turnout and motivation.”

The two most important counties in Markey’s district are Larimer and Weld, where a majority of the voters reside. Coming from Yuma County in the High Plains to the east, Gardner lacks a home base in the most critical area of the district.

Larimer County GOP Chairman Larry Carillo said Tuesday’s primary provided crystal-clear evidence of voter excitement, and its effect in Weld and Larimer counties. Norton won the Republican stronghold of El Paso County, home of Colorado Springs, yet lost the nomination. Carillo called that a “very rare” circumstance and chalked it up to Buck’s big wins in Weld (77 percent of the vote) and Larimer (64 percent), where Republican enthusiasm is high.

Colorado’s 4th district has been a top target for Republicans since election results poured in in November 2008. It had been 35 years since a Democrat held the seat, yet Markey defeated then-Rep. Marilyn Musgrave by 12 points. John McCain won the district, but it was by less than 3,000 votes.

The district is once again a target for the Defenders of Wildlife, an environmental group that spent more than $1 million to help oust Musgrave in 2008 and is defending Markey this year. The Democratic Congressional Campaign Committee is also watching closely as it works to protect the party’s House majority.

“It won’t come from Ken Buck, but with Cory Gardner running a campaign rife with hypocrisy, including [Wednesday’s] revelation about Gardner criticizing government subsidies while simultaneously benefiting from them, Gardner will obviously need all the help he can get,” DCCC spokesman Andy Stone said.

The National Republican Congressional Committee views Buck as a boon for Gardner in those populous counties.

“In Weld and Larimer counties, Democrats won’t be able to compete against Buck’s strong home base and Gardner’s star power throughout the district,” NRCC spokeswoman Joanna Burgos said. “Buck is very helpful for Republican candidates in the two counties, and Gardner is incredibly popular in the Eastern Plains, where he will surely be an asset for many other statewide candidates.”

As it was in 2006 and 2008, the 4th district is again a battleground for both parties. Unlike the past two election cycles, however, the national mood now favors Republicans.

“Ken Buck’s presence atop the ballot could help Cory Gardner at the margins,” Sondermann said, “though this factor pales in comparison to the national tailwind that both Buck and Gardner are counting on to propel them.”