President Donald Trump, fresh from a round of diplomacy with Japan’s prime minister, renewed a feud with billionaire Mark Cuban on Sunday, a familiar foil with whom he’s sparred in the past.

As the world grappled with North Korea’s latest act of aggression —firing off a new ballistic missile—Trump harangued the outspoken investor in a series of early morning tweets. Along with defending his crackdown on immigration, Trump blasted Cuban as being “not smart enough” to be leader of the free world.

For his part, Cuban —who supported Democratic contender Hillary Clinton in the general election—dismissed the broadside with a simple “LOL”. However, Cuban then tweeted an image of a 2016 letter he wrote to Trump, offering him support while imploring him to master the issues he would face as president.

It wasn’t immediately clear why Trump lashed out at Cuban, seemingly without provocation. At the height of the general election, the Dallas Mavericks owner was once approached by a group of dissident Republicans to run as an independent candidate, a move Cuban ultimately ruled out.