Earlier this year, Wedbush Securities trader Ian Winer warned that the stock market could lose half its value if Donald Trump were to win the presidency.

He said Trump’s “third-grade economics” would be “bad for home builders, bad for everybody, but most of all bad for the United States of America.”

Mark Cuban isn’t that much more bullish on the presumptive Republican presidential nominee.

Still, the billionaire reality-TV star said in an interview on CNN Monday night that Trump in the White House would likely mean disaster for stocks DJIA, -0.87% SPX, -1.11% COMP, -1.07% .

“I can say with 100% certainty that there is a really good chance we could see a huge, huge correction,” he said. How huge? More than 20%. Cuban explained that the uncertainty Trump would bring to the White House is “the last thing Wall Street wants to hear.”

Trump is “probably not as smart as he thinks he is,” he added.

So, Democratic front-runner, Hillary Clinton, is the better choice?

“The devil you know is better than the devil you don’t know,” Cuban said. “I can go to Hillary’s websites and there’s spreadsheets, there’s depth, there’s analysis, there’s details.”

Read: 5—and only 5—things that pose a greater global risk than a Trump presidency.

Cuban’s name has bandied about this week as a possible candidate, with a group of Republicans, including Mitt Romney, seeking an independent candidate to derail Trump’s plans.

Cuban told the Washington Post that he doesn’t see that happening.

“There isn’t enough time,” he said.

As for Trump, no Twitter response yet. He’s too focused on “Crooked Hillary”: