There are a lot of things about the 2016 election that nobody saw coming, and one of them is that international trade policy is likely to be a major issue in the presidential campaign. What’s more, the positions of the parties will be the reverse of what you might have expected: Republicans, who claim to stand for free markets, are likely to nominate a crude protectionist, leaving Democrats, with their skepticism about untrammeled markets, as the de facto defenders of relatively open trade.

But this isn’t as peculiar a development as it seems. Rhetorical claims aside, Republicans have long tended in practice to be more protectionist than Democrats. And there’s a reason for that difference. It’s true that globalization puts downward pressure on the wages of many workers — but progressives can offer a variety of responses to that pressure, whereas on the right, protectionism is all they’ve got.

When I say that Republicans have been more protectionist than Democrats, I’m not talking about the distant past, about the high-tariff policies of the Gilded Age; I’m talking about modern Republican presidents, like Ronald Reagan and George W. Bush. Reagan, after all, imposed an import quota on automobiles that ended up costing consumers billions of dollars. And Mr. Bush imposed tariffs on steel that were in clear violation of international agreements, only to back down after the European Union threatened to impose retaliatory sanctions.

Actually, the latter episode should be an object lesson for anyone talking tough about trade. The Bush administration suffered from a bad case of superpower delusion, a belief that America could dictate events throughout the world. The falseness of that belief was most spectacularly demonstrated by the debacle in Iraq. But the reckoning came even sooner on trade, an area where other players, Europe in particular, have just as much power as we do.