Last month, at the Peterson Institute for International Economics in Washington, D.C., AFL-CIO President Richard Trumka gave a 29-minute speech in opposition to the Trans-Pacific Partnership (TPP), a massive 12-country trade agreement that the Obama Administration hopes to complete this year. “At the end of the day, the partisan battles are really just so much noise,” he said. “For me, it’s all got to come back to one simple question: Is our trade policy working for America’s workers and for our nation as a whole? And the simple answer to that question is it isn’t.”

In their debate afterward, Trumka and Adam Posen, the president of the host institute and a supporter of the TPP, sometimes couldn't even agree on basic facts, like how many manufacturing jobs Germany has lost in the past 20 years. Often they resorted to generalizations instead: At one point in the largely cordial conversation, Trumka said to Posen, “I know you are a dyed-in-the-wool free trader. If I cut you open, little NAFTA balls would fall out of you.”

The crowd laughed, but the remark represents what makes trade agreements so impossible for policy journalists to understand. Opponents of the TPP like Trumka insist that its supporters think just about any free trade agreement will be good for the United States, regardless of its details. On the other side, supporters of the TPP insist they’ve learned from the failures of NAFTA; this time, they say, the trade agreements will benefit American workers.

Who is right? I don't know—and I’m not the only one. Writing at Vox, Ezra Klein said he was in the “undecided camp,” while Matt Yglesias called the TPP “one of the most frustrating things to cover in my career.” New York Times columnist Paul Krugman came out against the deal, while wondering why the president is spending so much political capital trying to pass it; David Wessel, writing for the Wall Street Journal, recently wondered why labor unions are working so hard to block it. If anything is clear about the TPP, it’s that no one knows exactly why everyone cares so much.

But talk to the key players in the debate, and it becomes clear that the TPP is the most important economic fight happening in Congress this year and one of the most important of Obama’s presidency. For once, it's not a partisan debate. Many on the right, including Representative Paul Ryan, support the deal, while the White House has faced the most intense criticism from members in its own party. The intraparty party fight often resembles the Trumka-Posen debate: high on rhetoric, short on substance. But it's possible to cut through the noise and discover the real issues at play. Here are the four most contentious parts of the trade pact: