The Trans-Pacific Partnership has detractors on both sides of the aisle, but the vast majority of congressional opposition comes from Democrats, even though the Obama administration has been giving it a pretty hard sell for the past nine months. And everyone understands Hillary Clinton's opposition to the TPP as at least in part motivated by her effort to beat Bernie Sanders in a primary.
Given all that, it might surprise you to learn that according to the most recent Pew poll, self-identified Democratic voters say they would be more likely to support a candidate who favors expanding trade deals.
The emerging party position, in other words, is being driven by the specific concerns of labor unions and a few other advocacy groups rather than the broad views of party members, which seem more driven by loyalty to Obama and a vague cosmopolitanism.
On the right, you see a similar dynamic around the question of tax cuts for the wealthy — an issue GOP elites are fanatically devoted to but which the electorate has mixed feelings on. But the mismatch for Democrats between what the interest group base wants and what the Democratic rank and file want is much larger in scale, albeit on a less significant issue.