[marc cuban] Mark Cuban thinks stocks could collapse into a bear market if Donald Trump becomes US president. The investor and reality-TV star told CNN on Monday that stocks could fall 20% if the presumptive Republican nominee wins in November. He said investors would not be able to put up with the uncertainty attached to a Trump presidency. "When you’re flip-flopping, when you’re not sure what the candidate’s going to say from one thing to another, that uncertainty potentially as the president of the United States — that’s the last thing Wall Street wants to hear," Cuban told CNN's Erin Burnett. "I can say with 100% certainty that there is a really good chance we could see a huge, huge correction" that could be as much as 20%, he said. Cuban told CNN that it seems Trump hasn't done extensive homework on some the economic issues facing America, including the ones he says he'll fix. But he gave Trump credit for shaking up the Republican establishment. He told CNNMoney last week that he had been asked to run against Trump, but thought it was too late. On Wall Street, fear is building about the elections in a year that started with a 9% stock-market plunge. It's almost one year since the market made all-time highs, which would be the longest streak in about three years. David Kostin, chief US equity strategist at Goldman Sachs, listed the election as one of six risks that could trigger a correction in the next few months. "The US presidential election is now part of every client conversation," Kostin wrote in a note last Friday. YOU CAN WATCH CUBAN'S FULL INTERVIEW WITH CNN HERE » SEE ALSO: AMERICA'S BIGGEST COMPANIES SAY THESE 4 THEMES ARE TOP OF MIND RIGHT NOW Join the conversation about this story » NOW WATCH: FORMER GREEK FINANCE MINISTER: The single largest threat to the global economy