U.S. President Donald Trump is reportedly considering promoting noted trade hawk Peter Navarro to the office of assistant to the president. This would be a significant move, and could signal Trump's intentions for trade policy.

In a way, that's good news. If Trump focuses on trade, where little of substance is likely to change, it could distract him from areas like health care and immigration where he could do more lasting damage. But Navarro's promotion, and the protectionist agenda it's likely to usher in, will probably not be very helpful for the U.S. economy.

First of all, Navarro has made at least one very basic mistake when talking about how trade affects the economy. He — like many other people — appears to believe that if trade deficits go down, economic output must rise. That's false.