Paul Krugman has what may well be the best column you will find about the politics of trade in the 2016 presidential elections. Anyone with interest in this issue should read the whole thing. A couple of excerpts:

The Sanders win defied all the polls, and nobody really knows why. But a widespread guess is that his attacks on trade agreements resonated with a broader audience than his attacks on Wall Street; and this message was especially powerful in Michigan, the former auto superpower. And while I hate attempts to claim symmetry between the parties — Trump is trying to become America’s Mussolini, Sanders at worst America’s Michael Foot — Trump has been tilling some of the same ground. So here’s the question: is the backlash against globalization finally getting real political traction?

If so, we can expect tweaks in messaging on the part of presidential, and perhaps down-ballot, candidates to amp up their protectionist cred. Krugman cautions, however:

You do want to be careful about announcing a political moment, given how many such proclamations turn out to be ludicrous. Remember the libertarian moment? The reformocon moment? Still, a protectionist backlash, like an immigration backlash, is one of those things where the puzzle has been how long it was in coming. And maybe the time is now.

Krugman critiques the overstated arguments of protectionists and globalists alike, and notes the limited ability of the candidates to do what they say about managing global trade. He concludes, however, by expressing his strong belief that “the case for more trade agreements — including TPP, which hasn’t happened yet — is very, very weak. And if a progressive makes it to the White House, she should devote no political capital whatsoever to such things.”
A sobering thought for voters — and for the leading candidates as they compete to win the support of American workers, a great many of whom have become deeply distrustful of U.S. trade policy.