WASHINGTON — After a decade of negotiations among a dozen nations, the trade deal known as the Trans-Pacific Partnership, or T.P.P., is almost complete and ready for final consideration by Congress. But before President Obama can present the final document for approval, Congress must vote to give him the right to limit consideration of the T.P.P. to a single up-or-down vote, with no filibusters or amendments allowed. That is called trade promotion authority, or T.P.A., and, so far, Mr. Obama has failed to get it.

Q.What is the T.P.P., and who wants it?

A. The T.P.P. is a 30-chapter document that promises to ease trade restrictions among the United States and 11 Pacific Rim nations, which together represent an annual gross domestic product of nearly $28 trillion, or 40 percent of the world’s G.D.P. It is being pushed by Mr. Obama, many Republicans and a handful of Democrats on behalf of American businesses, who say it will open lucrative new markets. Critics, including most Democrats, say it is a giveaway to big business that will encourage companies to shift manufacturing jobs to low-wage nations.

Q.Why doesn’t Congress just vote on the T.P.P. when it is finished?

A. After years of mostly secret talks among the United States and other nations, the deal would unravel if United States lawmakers had the right to amend it. So backers are pushing to give the president T.P.A. — the ability to present the agreement as a take-it-or-leave-it decision. Lawmakers could not filibuster or amend the deal, but they could reject it. That is the way previous trade deals, including the North American Free Trade Agreement, or Nafta, were approved in Congress. If Mr. Obama doesn’t get T.P.A., he is certain to leave office without the trade deal he says is critical to the American economy’s long-term health.