LEXINGTON, Ky. (AP) — Republican U.S. Sen. Rand Paul says he "can't imagine" voting for a Supreme Court nominee from Hillary Clinton, but stopped short of vowing to continue a blockade of Democratic appointments during the first and only televised debate with challenger Jim Gray.

Paul, who is seeking re-election in Kentucky after his failed bid for the Republican presidential nomination, said he would invite any Clinton nominee to his office for a "private discussion" and said he would support anyone who "pledges to uphold the separation of powers."

"It is going to be very difficult for me to vote for a candidate who is coming forward saying they want to abuse the Constitution," he said. "I can't imagine voting for a Clinton nominee unless she would appoint somebody that actually were someone who believes in the separation of powers as the founders wrote into the Constitution."

Paul's pledge to meet with a Democratic Supreme Court nominee is more than some of his colleagues in the Republican-controlled Senate has done. Led by Senate Majority Leader Mitch McConnell, also of Kentucky, the Senate has refused to fill a vacancy on the Supreme Court simply because it occurred less than a year from the presidential election. Since then, other Republican senators — including Ted Cruz of Texas and John McCain of Arizona — have suggested a Republican-controlled Senate would block any Democratic nominee indefinitely.

Gray, the mayor of Lexington, criticized Paul and other Republicans for not considering Obama's nominee, calling it "another example of gridlock and dysfunction."

"The Constitution is pretty clear on this. The president makes the nomination, and the Senate then takes up that nomination through and advice and consent process," Gray said. "I think the Senate should have done its job."

The exchange was one of several fiery moments of what has otherwise been a quiet Senate campaign. Paul mostly stuck to the script of Republican campaigns in conservative Kentucky by landing most of his punches on Clinton and Obama. He made sure to note Gray's support of Clinton's presidential campaign at every opportunity, even going so far to say it disqualified Gray from representing Kentucky in the Senate.

"Sen. Paul has already mentioned Hillary Clinton three times. That tells me that he is still obsessed about the presidential campaign," Gray said. "He's still thinking about the presidential campaign, he's not thinking about Kentuckians and Kentuckians' needs and challenges and problems. That's what I'm committed to."

Gray then turned to Paul and asked him to commit to serving a full, six-year term in the Senate if he is re-elected. That prompting Paul to call Gray a hypocrite — one of the few times he has engaged Gray during this campaign — by pointing out he would not be able to complete his full term as mayor if he were elected.

"If anybody up here is distracted by running for two offices, it's you," Paul said. "Why don't you take a pledge to do your job as mayor?"

Gray tried to pin down Paul on several of his Senate votes, including voting against funding for a bill to treat opioid addiction and his opposition to a bill that would rescue the pensions and health benefits of retired union coal miners.

"Sen. Paul said he's against it because it's not perfect. He's always letting the perfect get in the way of good. This is a big problem," Gray said.

Paul said he supports the concept of the bill to rescue miners' pensions, but wants to include provision that would scale back some of Obama's energy policies. He defended himself against Gray's charge that he was an obstructionist, pointing out his work with Democratic Sen. Cory Booker on criminal justice reform and Sen. Barbara Boxer on making it easier for companies to bring their overseas profits back into the country.

"I have a strong record of working with people on the other side," he said.