Final negotiations over the trade deal, the Trans-Pacific Partnership, are not like a checkers game with Congress, pitting two branches of government and two parties against each other. Rather, all 12 nations are asserting their particular economic and political interests in a multiple-dimension chess match, with one problem often setting off another.

Whether all of those can be resolved is now a matter of will. But the disagreements are pushing any resolution of the trade deal further into the politically difficult presidential election season in the United States. At least one negotiator suggested privately that it soon may become easier to say “no” than “yes.”

“The process of reaching a complicated trade agreement is to start with a huge number of uncertainties and slowly resolve them piece by piece until you can see one or two of the most difficult issues remaining,” said Tim Groser, New Zealand’s trade negotiator. “Now that the undergrowth has been cleared away, we can see clearly that there are one or two really hard issues.”

From dairy and sugar to autos and pharmaceuticals, the issues number more than one or two.

Vietnam is not ready to give up all the advantages that the communist country’s state-owned enterprises enjoy. Japan is still worried about Australia’s legal action against its treatment of marine mammals. And Chile, which already has free trade agreements sealed with each of the other members of the T.P.P., doesn’t see much of a loss in letting it all fall apart.

“To get one set of rules across 40 percent of world G.D.P., 33 percent of world trade, 12 disparate countries from Brunei all the way through the United States” was never going to be easy, said Andrew Robb, Australia’s minister of trade and investment.