Biden’s record on trade is already drawing attacks from the left and right. Of the 22 Democrats running for president, he’s the only one who voted for Nafta. The 1993 pact reduced barriers with Mexico and Canada, increasing trade and economic growth in all three countries. But it also led to an exodus of U.S. manufacturing jobs to Mexico and hurt wages for U.S. workers who held on to their jobs. Throughout the 2016 presidential campaign, Trump pilloried Nafta as a “disaster” and “the worst trade deal ever,” a message his top advisers believe was pivotal in helping him carry critical Rust Belt states once considered Democratic strongholds.

“Nafta still resonates in the industrial Midwest and Rust Belt,” says Stanley Greenberg, a veteran Democratic pollster who recently conducted focus groups on trade in Michigan and Wisconsin. “There’s still a lot of anger because it symbolizes, for many people, the indifference about the outsourcing of jobs and the favoring of elite economic interests in international trade agreements.”…

Since Biden declared his candidacy on April 25, his most vocal critics on trade have been on the left. Vermont Senator Bernie Sanders, who voted against Nafta as a congressman and is aiming to appeal to the same voters in the Upper Midwest, has repeatedly highlighted Biden’s history on trade. “It’s no secret that the most likely path to victory for Democrats in 2020 is to win the states Hillary Clinton won and then to add Wisconsin, Michigan, and Pennsylvania,” says Jeff Weaver, a senior adviser to the Sanders campaign. “Nafta devastated all three of those states. That will be litigated in the Democratic primary—as it should be, because it will certainly be litigated in the general election.”