Warren and Sanders can’t easily follow Scholten’s advice. While both senators have criticized the way Trump has implemented his trade policies, they’ve supported trade barriers in general. In outlining her trade policy last month, Warren declared that “tariffs are an important tool.” In March of last year, she called them “one part of reworking our trade policy overall.” When Trump imposed tariffs on foreign steel and aluminum last June, Sanders said, “I strongly support imposing stiff penalties on countries like China, Russia, South Korea and Vietnam to prevent them from illegally dumping.” While Harris hasn’t praised tariffs, she’s come out against NAFTA and TPP.

With a deeply unpopular trade war tanking the economy, these views are now a political liability, especially in Iowa. By attacking not merely Trump’s implementation of tariffs but the very notion that tariffs benefit America, Biden could link himself to Barack Obama and link his progressive challengers to Trump. Instead of backing off his long record as a free trader—as Hillary Clinton did when she flip-flopped on the TPP in 2016—he could argue that America’s mounting economic woes are proving him right.

They are. Trump’s tariffs have not revived American manufacturing. To the contrary, according to Mark Zandi, chief economist at Moody’s Analytics, they’ve already cost the United States 300,000 jobs. And they’re based on a series of wildly exaggerated claims about the way China “cheats” on trade.