Former Colorado State University athletic director Jack Graham has made the primary ballot for the Republican U.S. Senate nomination to run against Democratic incumbent Michael Bennet, Secretary of State Wayne Williams announced Wednesday morning.

Graham joins El Paso County Commissioner Darryl Glenn on the June 28 ballot. Glenn stunned political observers April 9 when he was the sole Republican to make it out of the state GOP assembly, where he won just over 70 percent of the delegate votes. Three other candidates have submitted petition signatures and are awaiting verification.

Graham was one of the last of 13 candidates to enter the primary race, declaring his candidacy at the end of January, but was the first of four GOP U.S. Senate candidates to turn in petition signatures. (Lakewood businessman Jerry Natividad entered the race a month later but went through the assembly process and failed to make the ballot.)

Of the 22,786 signatures collected by the Graham campaign, the secretary of state’s office ruled that 12,891, or just over 56 percent, were valid. Colorado law requires a total of 10,500 valid signatures —1,500 from each of the state’s seven congressional districts — to make the primary ballot for statewide offices. Graham came closest to clearing the hurdle in the 3rd Congressional District, where he had just 1,687 valid signatures, and 1,416 were ruled invalid, the secretary of state’s office said.

“Ginger and I are grateful for all the help and support so many Coloradans volunteered in our successful quest to petition onto the primary ballot,” said Graham in a statement. “We look forward to the primary election campaign and making our case to be the Republican nominee for U.S. Senate.”

The other three Republicans seeking the ballot by petition are former state Rep. Jon Keyser, R-Morrison, Colorado Springs businessman Robert Blaha and former Aurora City Councilman Ryan Frazier. The secretary of state’s office is verifying their signatures in that order, the order they were submitted, and has until April 29 to issue a determination.

Bennet was nominated to the Democratic primary ballot without opposition Saturday at his party’s state assembly in Loveland.

— ernest@coloradostatesman.com