Former Federal Reserve Chairman Alan Greenspan called President Donald Trump’s tariff policies “insane” and said “why we’re doing it probably is very deep in the psyche of somebody.”

Responding to a question about China at an event at New York University on Wednesday, he said both sides lose out in such a clash.

“There are victors and there are losers in a tariff fight,” Greenspan said. “But that doesn’t say that a more important issue is both are losing, it’s just the winner loses less.”

“It’s an excise tax, and people think of tariffs other than what it is,” he added. “It’s a tax, and everybody engaged in warfare of this type, it would mean that you’re withdrawing credit or purchasing power from a whole series of countries.”

Greenspan said the notion that China would outrace the U.S. in all economic respects “is a mistake,” pointing to their lower gross domestic product per capita.

The U.S. and China have levied several rounds of tariffs on each others’ goods, and tariffs on $200 billion of Chinese imports are due to rise to 25 percent in January in the absence of a breakthrough in negotiations.