WATCH: Sen. Mike Lee explodes when conservative TV host demands Trump endorsement

Republican Sen. Mike Lee hasn't endorsed Donald Trump -- and he has a lot of reasons why.

The Utah senator appeared on NewxMaxTV, where host Steve Malzberg asked why he wasn't "trumpeting Trump."

“Hey look, Steve, I get it -- you want me to endorse Trump,” Lee said. “We can get into that if you want."

Lee then listed several reasons why he couldn't back Trump, who became the GOP's presumptive nominee after Sen. Ted Cruz (R-TX) dropped out of the race in May.

"We can get into the fact that he accused my best friend’s father of conspiring to kill JFK," Lee said. "We can go through the fact that he’s made statements that some have identified correctly as religiously intolerant. We can get into the fact that he’s wildly unpopular in my state, in part because my state consists of people who are members of a religious minority church -- a people who were ordered exterminated by the governor of Missouri in 1838 -- and statements like that make them nervous.”

Even so, the Republican senator said Trump could still win his endorsement.

"These statements are not something I could not get over, if I heard the right things out of him," Lee said. "But if you want to go into why I have concerns, I could go on if you'd like. I hope I can get over these concerns, I hope Mr. Trump can help me identify them. But don’t sit here and tell me, Steve, that I have no reason to be concerned about Donald Trump."

Malzberg insisted he wouldn't tell the senator to do anything, but he then said he would think that Lee should be more concerned about Hillary Clinton than Trump.

"She's under FBI investigation, she takes money from countries that kill gays, that treat women like garbage, you know about the email scandal -- the list goes on -- the Clinton Foundation, the conflict of interest, the corruption, the lifelong corruption, it goes on and on and on," Malzberg said. "The first thin on your list -- again, with all due respect -- he said that my best friend's father, you know, killed Kennedy or was involved in it. So I hope it's not personal."

Lee pointed out that Trump had actually leveled that accusation "without any scintilla evidence," and he said that concerned him.

"I hope I can get over this, because I can't vote for Hillary -- I know there's no possibility of that," Lee said. "What I am saying is that Donald Trump can still get a lot of votes from a lot of conservatives like me, but I would like some assurances on where he's going to stand his ground. I would like some assurances that he is going to be a vigorous defender for the U.S. Constitution, that he's not going to be an autocrat, that he's not going to be an authoritarian -- that he's not going to be someone that's going to abuse a document to which I've sworn an oath to uphold and protect and defend. I'm sorry, sir, but that is not an unreasonable demand.

Watch the entire segment posted online by NewsMaxTV: