Republican U.S. Senate candidate Jon Keyser is planning to petition onto the primary ballot, sources with his campaign have confirmed to The Colorado Statesman.

Keyser is the fourth Republican candidate petitioning for the nomination to challenge U.S. Sen. Michael Bennet, the lone Democratic incumbent considered vulnerable in this year’s Senate races.

“It’s going to take a conservative movement to defeat Sen. Michael Bennet, and I’m committed to building a grassroots army that not only includes those who have fought conservative battles for generations, but also one that brings new activists into the fold,” Keyser told The Colorado Statesman on Friday.

“We can’t afford to leave behind any voter or grassroots activist who is dedicated to defeating Senator Bennet, and that’s why I’m pursuing an inclusive ballot strategy to activate grassroots conservatives across Colorado,” Keyser said.

Keyser, an attorney and decorated Air Force reservist, resigned his House District 25 seat in Jefferson County last week and stepped down from his job at the international law firm Hogan Lovells in order to devote full time to campaigning.

Another nine candidates are either going through the caucus and assembly process or haven’t revealed their plans. Candidates can petition on to the June 28 primary ballot by gathering 1,500 valid signatures from each of the state’s seven congressional districts or qualify at the GOP state assembly in April with the support of at least 30 percent of delegates.

It’s the most crowded primary field in the country and could be the most crowded statewide primary ballot in memory.

Keyser supporters say he’ll bring a focus on national security issues to the race and can tap the deep pockets of Republican donors in order to challenge Bennet, who headed the Democratic Senatorial Campaign Committee in the last cycle and reported more than $6.7 million in the bank at the end of the year.

Just this week, Republican senate candidates Ryan Frazier, Robert Blaha and Jack Graham pulled petitions for the primary. Candidates can start circulating petitions on Monday and have until April 4 to collect enough signatures.

The other candidates in the running include state Sen. Tim Neville, R-Littleton, El Paso County Commissioners Darryl Glenn and Peg Littleton, Jefferson County Commissioner Don Rosier, Charlie Ehler, Tom Janich, Michael Kinlaw and Jerry Eller. Business leader Jerry Natividad has said he plans to announce his campaign by the end of January.

At a meeting of the Jefferson County Republican Party central committee in Lakewood on Wednesday, Keyser called Bennet “a dangerous guy” and promised that “the contrasts will be very, very clear” with Bennet.

Referring to Bennet, Keyser told the crowd of Republicans, “He’s dangerous, he’s a dangerous guy. A lot of people don’t know a lot about his voting record, but I’ll tell you a couple things you should know.”

“I’ve spent my entire life in national security and foreign policy issues,” Keyser said, adding he plans to “be absolutely relentless relentless, because the safety and security of our country is the absolute No. 1 job of the federal government.”

“The first thing that really concerns me — this is a personal thing to me,” Keyser said. “Michael Bennet voted to give $100 billion to the largest sponsor of terror in the world, $100 billion. And then, a couple of days ago, you’ve got (Secretary of State) John Kerry in the White House saying, yeah, we know that’s going to fund terror around the world.” Then, after pausing for a moment, Keyser continued: “That’s personal to me because, when I served in Iraq and Afghanistan, Iranian insurgents killed my friends.”

State Democratic Party spokesman Andrew Zucker dismissed Keyser’s chances when he announced he was running two weeks earlier.

“The (National Republican Senatorial Committee) lost all of their top recruits to run for Senate in Colorado before they settled on Jon Keyser, and are now headed toward a crowded and divisive and damaging primary. No matter who emerges on their side, Michael Bennet will win in November because he’s worked across party lines to get things done for Colorado.”

— ernest@coloradostatesman.com