The Trans-Pacific Partnership, the largest regional trade accord in history, would set new terms for trade and business investment among the United States and 11 other Pacific Rim nations — a far-flung group with an annual gross domestic product of nearly $28 trillion that represents roughly 40 percent of global G.D.P. and one-third of world trade.

But the agreement, which requires the approval of Congress, has become a flashpoint in the United States presidential campaign, opposed by the nominees of both major parties as a symbol of failed globalism and the loss of United States jobs overseas.

The product of years of negotiations that culminated last fall with the endorsement of the 12 nations’ trade chiefs, the Trans-Pacific Partnership was a hallmark victory for President Obama, who has pushed for a foreign policy “pivot” to the Pacific rim. It seeks to bind Pacific nations closer through lower tariffs while also serving as a buttress against China’s growing regional influence. An independent study said that it would raise incomes and exports in the United States, but not jobs over all.

Many Democrats in Congress have voiced skepticism over the benefits. And opposition to the pact became a popular rallying cry in stump speeches by both Donald J. Trump, the Republican nominee, who has promised to tear up the deal, and Bernie Sanders, who argued during the Democratic presidential primaries that it would lead to a loss of jobs and competitive wages.