Both Bill Clinton and Barack Obama pushed free trade deals as president, but both faced massive resistance from Democrats in Congress. And in the 2016 campaign, both Hillary Clinton and Bernie Sanders came out against Obama's Trans-Pacific Partnership deal — for Clinton, a very rare break with the White House.

But a new Pew survey confirms that trade deals are broadly popular in the United States, especially with Democrats, and including with supporters of both Sanders and Clinton.

This is consistent with the view that such deals may have been very bad for a minority of Americans — people with jobs in Asia-competing factories and residents of communities built around such factories — who may be the only people for whom trade is actually a voting issue.

But this is important context for the future of trade policy, and raises the prospect that a Trump-Clinton general election could produce a larger realignment with Democratic officeholders joining rank-and-file Democrats in embracing trade deals while Republicans oppose them.