Gardner’s announcement deals a heavy blow to the Colorado Republican Party, which now fields no candidates in the race for Udall’s seat. 

A number of prominent state Republicans have already declined a bid, including outgoing Attorney General John Suthers, Weld County District Attorney Ken Buck and Rep. Mike Coffman. 

Gardner’s decision to bow out may indicate early recruiting struggles for the state GOP, lending momentum to Udall’s reelection campaign.

"This news does not come as a surprise considering Senator Udall's long record of achievements, his bipartisan approach and his strong support from Coloradans," said the senator's spokesman, Mike Saccone, according to the Post

Justin Barasky, national press secretary for the Democratic Senatorial Campaign Committee, said Gardner's decision is just the latest example of the national Republican Party’s failed attempt at outreach ahead of 2014.

Cory GardnerCory Scott GardnerThe Hill's Morning Report - Trump touts new immigration policy, backtracks on tax cuts Hickenlooper announces Senate bid Poll: Trump trails three Democrats by 10 points in Colorado MORE’s decision not to run for Senate in Colorado is a recruitment failure that’s emblematic of the inability of national Republicans to expand the map outside of the red states this cycle,” Barasky told The Hill in an statement. 

“Senator Udall enjoys strong support across the state of Colorado thanks to his well earned reputation as a fighter for Colorado jobs and middle class families.”

The National Republican Senatorial Committee pushed back, pointing out that Democrats have had their share of recruiting failures.

 “The two biggest recruiting failures this cycle occurred when the Democrats pleaded with [Rep.] John BarrowJohn Jenkins BarrowRepublican wins Georgia secretary of state runoff to replace Kemp The most important runoff election is one you probably never heard of Our democracy can’t afford to cut legal aid services from the budget MORE [D-Ga.] and [former South Dakota Rep.] Stephanie Herseth Sandlin to run [for the Senate] and failed,” NRSC Communications Director Brad Dayspring said in a statement to The Hill.

Dayspring added that in a post-Citizens United world, it is more important to find the right candidate than it is to “rush through the process and fail as the Democrats have done.”

Updated at 4 p.m. and 4:20 p.m.