Jon Keyser’s bid for U.S. Senate ran away from him Thursday after the Republican candidate dodged repeated questions about forged signatures used to qualify for the ballot and gave a cringe-worthy interview that included a menacing comment toward a reporter about his Great Dane, Duke.

The dog-bites-candidate moment came at a debate hosted by a Foothills Republican club just days after a local television station uncovered problems with Keyser’s petitions for the June primary ballot.

The debate’s first four questions involved the petition issue, and Keyser refused to answer all of them.

“Here’s the important thing. I’m on the ballot, and I’m going to beat Michael Bennet,” Keyser said in a line he repeated five times in two minutes.

The response drew groans from the crowd and a shot from GOP rival Darryl Glenn who said the issue is important to the candidate’s integrity.

“If you are going to stand for the rule of law, if you are going to raise your hand and support the constitution, then you need to follow the law,” Glenn said to applause. “That’s the issue.”

In an interview with The Denver Post and Denver7 during a break, Keyser dodged eight more questions on the issue.

He took the issue a step further when he criticized the local TV reporter for “creeping around my house” after the reporter knocked on the door at his home to request an interview.

“You woke up my kids,” Keyser told the reporter. “Yeah, you woke up my kids. My baby cried for an hour after that. Did you get to meet my dog?”

“I met your dog and your nanny. She was very kind,” Denver7’s Marshall Zelinger responded.

“My dog, he’s a great dog. He’s bigger than you are. He’s huge,” Keyser said. “He’s huge. He’s a big guy. Very protective.”

“What did you mean by his size?” Zelinger responded.

“Did you see him? He’s a Great Dane. He’s 165 pounds,” Keyser continued.

The exchange — and the candidate’s continual refusal to address the signature — made headlines in national political circles, and Democrats pounced, calling it a “painful meltdown.” His repetitious answers drew comparisons to Marco Rubio, who drew ridicule in presidential debates for his robotic answers.

Keyser made the ballot only after winning a legal challenge involving his petitions. The Colorado secretary of state’s office said he finished 86 signatures short of the 1,500 needed in the 3rd Congressional District. But he presented new evidence in court to legitimize the signatures, and a judge put him back on the ballot.

Keyser’s refusal to discuss the forged-signature issue disappointed Ray Warren, a Jefferson County Republican who attended the forum.

“If somebody forged the signature on there, shame on them, but it’s not necessarily his fault,” the 69-year-old retiree said. “If we want to be honest and we want politicians who are honest, just face the facts and say it like it is.”

Another Republican candidate, Ryan Frazier, is still fighting to join the four other candidates after he didn’t submit enough valid voter signatures to qualify.

Frazier’s campaign is challenging the ruling, and the Colorado Supreme Court agreed Thursday to hear the case.

John Frank: 303-954-2409, jfrank@denverpost.com or @ByJohnFrank