(CNN) - A fellow Democrat warned Kentucky Senate candidate Jack Conway that his latest ad targeting Republican Rand Paul's reported behavior in college is "very dangerous."
Sen. Claire McCaskill, D-Missouri, said the Conway ad that repeats an unsubstantiated GQ story about Paul when he was a student at Baylor University comes "close to the line" in what should be deemed inappropriate in political campaigns.
"Candidates who are behind at the end reach, and sometimes they overreach," McCaskill said on MSNBC. "This ad is very dangerous because it reaches back to college. The ad came close to the line."
The spot hit Kentucky airwaves over the weekend and references the story that - relying on anonymous sources - reported Paul blindfolded and tied up a female student, forcing her to take bong hits. The story also reported Paul told the woman his god was "Aqua Buddha" and that she should bow down and worship him.
Responding to the report in August, Paul said he did not remember the event and added, "I really don't think that politicians should be asked to answer anonymous accusers from 27 years ago, but I will categorically deny that I ever kidnapped anyone or forced anybody to use drugs."
But the new spot from Conway says Paul still hasn't adequately addressed the matter:
"Why was Rand Paul a member of a secret society that called the Holy Bible 'a hoax' - that was banned form mocking Christianity and Christ?" asks the narrator in the ad called “Why?” "Why did Rand Paul once tie a woman up? Tell her to bow down before a false idol and say his god was 'Aqua Buddha?"
Paul expressed outrage over the commercial at a Kentucky Senate debate Sunday night, asking Conway, "Have you no decency? Have you no shame?"
"You know how we know when you're lying? Your lips are moving," an angy Paul also said. "You're accusing me of crimes. Do you know nothing about the process? You're going to stand there and accuse me of a crime from 30 years ago from some anonymous source? How ridiculous are you? You embarrass this race."
Paul refused to shake Conway's hand at the end of the debate.
Conway, the state's attorney general, defended the ad during Sunday's debate, saying Paul had still not answered the "fundamental questions" the commercial raises.
But despite McCaskill's unease with the commercial, she said the Tea Party-backed Paul is "out there."
He's an extreme candidate," she said.
Polls show Paul holds a single-digit lead over Conway.