Trump: Mark Cuban is 'not smart enough to run for president'

President Donald Trump tweeted Sunday morning that Mark Cuban is "not smart enough to run for president." 

"I know Mark Cuban well. He backed me big-time but I wasn't interested in taking all of his calls," Trump tweeted. 

The tweet appears to be a response to Cuban's comments in an interview with The Star-Telegram Friday.

Referencing the outrage in response to Under Armour CEO Kevin Plank's recent comment that "To have such a pro-business president is something that is a real asset for the country," Cuban said that he has advised CEOs to avoid making public political statements.

Several prominent Under Armour-sponsored athletes, including Steph Curry and Misty Copeland, spoke out against Plank's comments on Trump.

"It's a tough situation for CEOs," Cuban said to The Star-Telegram. "You want to make nice with the president because you're a public company and you have shareholders, and it's hard to balance doing the right financial thing versus doing what they think is the right thing, whatever your political beliefs are. It's not an easy position to be in."

He added: "Do what you think is right. Be an American citizen first."

Cuban responded to Trump's Sunday morning tweet with a tweet of his own, which appears to show a correspondence between the two last spring. In an email to Trump via speechwriter Meredith McIver dated May 8, 2016, Cuban wrote, "You don't have to bore people with details. But you have to learn the details. Everyone else is afraid of you. I like to challenge you." 

According to the report in the New York Post, Cuban is one of four Democrats whom The White House views as potential challengers to Trump in 2020.

Cuban had returned to publicly voicing his opinions about Trump - something he frequently did during the campaign - following the president's January executive order temporarily banning travel from seven majority-Muslim nations to the US and from all refugees hoping to enter the US. In the process, he has become the face of opposition to Trump in the business and tech community, taking a more active stance against the president than any prominent executive.

"I've been crushing POTUS," he announced on Twitter at the end of January. "He has earned it."