Mark Cuban never did hear back from Donald Trump.

But the NBA owner and "Shark Tank" star, who offered to give $10 million to charity if Trump would sit for a four-hour policy interview, isn't letting up on his criticism of the Republican presidential nominee.

Cuban called Trump "an immediate and present danger" to the country in an interview with CNNMoney's Alison Kosik.

"He has yet to demonstrate that he can keep his mouth shut at the right time," Cuban said. "That scares the s--- out of me."

Cuban has long been a critic of Trump, who he says will cause U.S. financial markets to "tank" if he's elected.

Related: Mark Cuban offers Donald Trump $10 million for a four-hour grilling

The billionaire businessman and Dallas Mavericks owner told CNNMoney that he made the $10 million charity offer because he doubts Trump understands his own policy proposals.

"I would just take his website, repeat it to him and have him explain it, and see if he can," Cuban said.

.1) @realDonaldTrump $10mm to the charity of YOUR choice if you let ME interview you for 4 hrs on YOUR policies and their substance. — Mark Cuban (@mcuban) September 16, 2016

Cuban also reiterated his endorsement of Hillary Clinton, the Democratic nominee, and attributed the public's lack of trust in her to a marketing problem.

"She's kind of boring. She doesn't come across as being charismatic," Cuban said. But he said he'd "rather have somebody who understands the issues" win the election.

Related: Mark Cuban: It would have been 'fun' to run against Donald Trump, but it's too late

Cuban brushed off a question about whether he'd consider his own run for the White House. The tech entrepreneur stirred that pot earlier this year when he told CNNMoney he was recruited to run against Trump.

Now?

"I guess never say never," he said. "But I have no interest at all, and don't see that changing."