A social media spat between Elon Musk and Jeff Bezos this week underscored a sharpening rivalry between two of the world’s richest men at a time when both are trying to grow their sprawling businesses empires in President-elect Trump’s second term.

The world’s two richest men are longtime business rivals, but now one of them has the ear of the next president of the United States.

Elon Musk reignited a public dispute with fellow billionaire and space-industry rival Jeff Bezos, saying the Amazon.com founder had said President-elect Donald Trump would lose the election and that people should sell stock tied to Musk.