Billionaire supporters of President Donald Trump—including Elon Musk—spoke out Monday morning and issued warnings about the economy as global stock markets plunged further in response to the escalating trade war.

Elon Musk appeared to split from the Trump administration on tariffs overnight — as he lashed out at trade adviser Peter Navarro and said he hoped for a “zero tariff situation” between the US and Europe.

Navarro, widely seen as the architect of Trump's tariff plans, told CNBC Musk had done a good job with his work to streamline government, but his opposition to duties was not surprising, the latest salvo in a growing feud between the Trump advisers.