While we don’t know the substance of what was discussed, Musk’s presence is a concerning preview of Trump’s often reckless approach to diplomacy — as well as his disregard for the line between private interests and public policy. There are a lot of reasons why Musk should be the last person hopping on that call.

After his 2016 election, Trump tapped Wall Street raider Carl Icahn as a "regulatory reform" adviser. He soon quit under a cloud of controversy.