The Colorado secretary of state’s office has given two more Republican U.S. Senate candidates the go-ahead to start circulating petitions for the June primary ballot, bringing to five the number of GOP candidates who could be gathering signatures for the race.

Jefferson County Commissioner Don Rosier and former state Rep. Jon Keyser, R-Morrison, both have had their petition formats approved, a spokeswoman for Secretary of State Wayne Williams said Monday, joining former Aurora Councilman Ryan Frazier, Colorado Springs business consultant Robert Blaha and former CSU athletic director Jack Graham of Fort Collins, whose petitions were OK’d last week.

In order to make the primary ballot for the Senate seat, candidates must turn in 10,500 valid signatures of Republicans, with 1,500 gathered from each of the state’s seven congressional districts. Candidates can start circulating petitions this week, and they’re due April 4.

In all, 13 candidates have declared they’re running for the GOP nomination to challenge Democratic U.S. Sen. Michael Bennet.

Four of the Republican candidates — state Sen. Tim Neville, R-Littleton, El Paso County Commissioners Peg Littleton and Darryl Glenn and activist Charlie Ehler of Fountain — have vowed to pursue the nomination through the caucus and assembly process. Candidates who take that route need the support of more than 30 percent of delegates at the April 9 state GOP assembly to qualify for the June 28 primary ballot.

Candidates who have pulled petitions could also pursue the primary ballot through caucuses and nominating assemblies, although the deadline to turn in petitions falls five days before the state assembly, so petitioning isn’t a viable fallback option for those who don’t make the ballot at assembly, as has been the case in years past.

Rosier was elected to his second term as a Jefferson County commissioner in 2014. Keyser was first elected to the state House that same year. He resigned his seat last month in order to campaign full-time for the Senate.

— ernest@coloradostatesman.com