Rep. Mike Coffman’s (R-Colo.) decision this week to pass on a Senate run has damaged Republican hopes of taking out Sen. Michael Bennet Michael Farrand BennetOVERNIGHT ENERGY: House Democrats tee up vote on climate-focused energy bill next week | EPA reappoints controversial leader to air quality advisory committee | Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' Senate Democrats demand White House fire controversial head of public lands agency Next crisis, keep people working and give them raises MORE (D-Colo.), their top incumbent target in 2016.



Coffman was the top recruit for national Republicans. He’s well known in the state, having won statewide elections twice, as treasurer and secretary of State, and represents a high-profile swing-district that encompasses the southern portion of liberal Denver.



He’s also a proven fundraiser and has consistently outperformed in one of the nation’s most competitive districts, most recently crushing former state House Speaker Andrew Romanoff, a top Democratic recruit, by 9 percentage-points on his way to reelection in 2014.



Without him, the GOP faces running an untested, second-tier candidate against a well-funded incumbent in a state that will be critical in determining which party controls the Senate in 2016.



“Coffman was the top draft pick,” said Jon Caldara, president of the conservative Independence Institute in Denver. “He’s a tough, old-school campaigner. Beyond him, there’s no heir apparent ready to step in.”



In 2014, Senate Republicans caught lightning in a bottle with now-Sen. Cory Gardner Cory Scott GardnerMcConnell locks down key GOP votes in Supreme Court fight Will Republicans' rank hypocrisy hinder their rush to replace Ginsburg? Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 MORE (R-Colo.), a former House member who turned out to be a top-level candidate. Gardner edged former Sen. Mark Udall Mark Emery UdallThe 10 Senate seats most likely to flip Democratic presidential race comes into sharp focus Democrats will win back the Senate majority in 2020, all thanks to President Trump MORE (D-Colo.), whose campaign made several strategic blunders, in a year that heavily favored Republicans.



Republicans in the state say few candidates have the political skills to match Gardner, but they believed Coffman came the closest.



“This is a blow, no doubt about it,” said former Colorado Republican Party chairman Dick Wadhams.



Senate Republicans are largely on defense going into 2016, a presidential year when turnout will likely favor Democrats. The GOP is protecting 24 seats, compared to only 10 for Democrats.



Democrats need to pick up five seats to reclaim the majority they lost in the fall, but that climb would become steeper if the GOP could steal a seat that Democrats are defending.



National Republicans have been eyeing Colorado — a purple battleground state with a fierce independent streak and history of ticket-splitting, as one of their best pick-up opportunities.



Along with Nevada, where Sen. Harry Reid Harry Mason ReidDemocrats fear Russia interference could spoil bid to retake Senate Graham signals support for confirming a Supreme Court nominee this year Trump signals he will move to replace Ginsburg 'without delay' MORE’s (D) retirement has made the battle for his seat a toss-up, Colorado is the only other state where Republicans can realistically go on offense.



“If Bennet is their top national target, they’re in trouble,” said Colorado political analyst Eric Sondermann. “He starts off in a stronger position than Udall and there are no Cory Gardners waiting on the Republican bench. Even with all of the advantages Republicans had in 2014, they still only won that Senate seat by less than two points.”



Coffman was the only viable potential candidate Republicans could look to from their ranks in the House.



Colorado’s GOP Reps. Scott Tipton (R-Colo.) and Doug Lamborn are both seeking reelection in the House. And newly-elected Rep. Ken Buck (R-Colo.) lost the Senate race to Bennet in a gaff-laden effort in 2010, a year when Republicans won every other competitive Senate race in the country.



Now, political watchers in the state expect a flood of untested state-level lawmakers, public officials and local businessmen will fill the void.



The best potential GOP candidate might be Coffman’s wife, Cynthia Coffman, who in 2014 won her first-term as attorney general. Cynthia Coffman was the second highest vote-getter in the entire state that year.



She could run for Senate and keep her current job, so the risk would be minimal. But many in the state believe she’s content in her new position and will not run for Senate.



State Sen. Ellen Roberts is another attractive potential candidate. Republicans believe she could be formidable in the general election, but the problem for Roberts will be getting through the GOP primary.



Roberts is a rare pro-choice Republican in Colorado, though Democrats have sought to exploit recent comments she made, muddying her position on the issue.



State Senate president Bill Cadman is another name Republicans mention in the top tier of potential candidates.



Other possibilities include State Sen. Owen Hill, former State Sen. Mike Kopp, conservative radio personality Dan Caplis, businessman Wil Armstrong — the son of former Sen. William Armstrong (R-Colo.) — businessman Robert Blaha — who lost a primary challenge to Lamborn in 2012 — and Steve Laffey, a Colorado transplant from Rhode Island who lost a primary challenge to former Sen. Lincoln Chafee in 2006.



Rising Republican star George Brauchler, the district attorney prosecuting the Aurora theater shooting case, will be tied up with that responsibility through the fall.



Walker Stapleton, the 41-year-old state treasurer, has said he’s more interested in running for governor.



“Coffman had the potential to clear the field before the fight really started,” said Caldara. “My concern is that Republicans here often have ugly primaries where they destroy any chance the eventual nominee has of nominee wining in the fall.

Still, Republicans believe Bennet is ripe for the ousting.



“Senator Michael Bennet is extremely vulnerable and Colorado is a top pickup opportunity for Senate Republicans in 2016,” National Republican Senatorial Committee spokesman Matt Connelly said in a statement.



They say he’s still relatively unknown across the state, point to his favorability rating, which is lower than Udall’s at this point in the last cycle, and call him an accidental senator, arguing he only won the race in 2010 because of Buck’s campaign missteps.

Republicans believe Bennet remains vulnerable. They say he’s still relatively unknown across the state, and call him an accidental senator, arguing he only won the race in 2010 because of Buck’s campaign missteps.



“I think there’s a scenario where someone terribly dangerous to Bennet could get nominated and catch fire,” said Wadhams. “There’s a strong possibility that the Republican presidential nominee will win Colorado. Look at the polling — voters don’t trust Hillary, and she’s no Obama. She won’t have the same appeal he had out here, which could greatly help our Senate nominee.”



Still, Republicans face an uphill climb.



Bennet will begin the race with a huge fundraising advantage over the eventual GOP nominee. He’s one of only a handful of senators to raise more than $2 million in the first quarter, a feat he’s likely to replicate every quarter going forward.



And Democrats, still stinging from the Udall loss, have mobilized early on the ground to protect Bennet.



“Coffman is a practical guy and pragmatist,” said Sondermann. “He read the tea leaves and realized the deck is stacked against Republicans in 2016.”

Correction: A previous version of this article stated that Cynthia Coffman was the highest vote-getter in Coloraod in 2014. She was the second highest vote-getter behind Gov. John Hickenlooper (D-Colo.).