House Democrats dealt a withering blow to one of President Barack Obama’s biggest policy priorities by voting against legislation they’d typically support: federal assistance to workers displaced by trade agreements. The bill was a necessary step for Obama to move forward with a sprawling trade agreement with Pacific Rim nations, known as the Trans-Pacific Partnership (TPP), so Democrats have effectively derailed the entire process.

It was a serious rebuke to Obama, who had come to Capitol Hill on Friday morning to lobby legislators personally; even House Minority Leader Nancy Pelosi voted against the bill, refused to rally the troops around it.

The fight isn’t over yet. After the defeat of the assistance package, Speaker John Boehner held a vote on a bill giving Obama fast-track trade promotion authority, which passed 219-211. The worker assistance portion still needs to pass, however, for Obama to move forward on the trade deal; the House GOP is expected to vote on it again next week. The White House will continue to search for Democratic votes and could try to squeeze some concessions out of House Republicans to bring more members over. 

But the opposition has been aggressive, organized, and unified: The House Democrats’ opposition today marked the culmination of a massive lobbying campaign led by labor unions, environmental groups, and other progressive advocates. Their arguments haven’t been limited to the long-standing criticism that free trade deals hurt American workers (though they’ve been adamant about that throughout). They object to a new corporate dispute mechanism that opponents argue will allow multinational corporations to undermine everything from Dodd-Frank financial regulations to food safety.

They’ve also decried the negotiation of the deal itself: It’s done in secret, and the few people authorized to read the proposed deal can’t discuss the specific terms. The rationale is that it’s impossible to negotiate a trade deal with other countries if everything is made public, but the secrecy has fueled the opposition from both the left and the right. And fast-track authority means that Congress only gets an up or down vote on the agreement—which is why conservatives have also rallied against fast-track, saying it gives Obama too much executive authority.

Obama and his GOP supporters have played up the purported economic benefits of the deal, but the president also sees the agreement as key to improving the U.S.’s geopolitical standing in Asia as a bulwark against China. Polls have also shown broad support for free trade, generally speaking, among Democratic voters. But the public has not been worked up about TPP either way, as polling also shows that most aren’t familiar with it.

Meanwhile, the opposition has aggressively targeted Democrats who’ve moved to support the deal. They’re also the very activists that Hillary Clinton is counting on to mobilize the party's base. Caught in between, Clinton has stayed mum about her position. That’s prevented her from taking too much direct fire on the issue, but it hasn’t helped the president she’s hoping to succeed.