President Trump wasted no time on social media Sunday morning, and one of several tweets was directed at Dallas Mavericks Owner Mark Cuban.

In that tweet, Trump said Cuban, who supported him during the early portion of the campaign, switched allegiances to Hillary Clinton because Trump didn’t return his phone calls:

Cuban came back with this:

This exchange likely occurred in response to Mark Cuban’s quotes in the Fort Worth Star-Telegram, where he advised CEOs about how they should talk about politics in the aftermath of backlash against Under Armour CEO Kevin Plank after he said President Trump’s business vision was a “real asset to the country.”

Cuban said, “It’s a tough situation for CEOs. 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.”

Cuban later added: “Do what you think is right. Be an American citizen first.”

Then, according to the Business Insider, Cuban took things a step further. “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.”

Mark Cuban is a rumored presidential contender for the Democrat nomination in 2020. Of course, that could have something to do with all this as well.

Follow Dylan Gwinn on Twitter: @themightygwinn