Mark Cuban: Donald Trump Becoming 'Stupider Before Your Eyes'

Businessman Mark Cuban continued his crusade against Donald Trump on Tuesday by targeting the presumptive Republican nominee's lack of substance and failed business ventures.

"It’s rare that you see someone get stupider before your eyes, but he’s really working at it," the billionaire and Dallas Mavericks owner told "Extra." "You have to give him credit. It’s a difficult thing to do, but he’s accomplished it.”