WASHINGTON — President Barack Obama expressed optimism Sunday that his trade pact with Pacific Rim nations would be approved by Congress, despite widespread opposition for the 12-nation deal.

Democrats and Republicans have soured on the Trans-Pacific Partnership as overseas trade has emerged as a campaign issue. Hopes for passage by the end of Obama's term have largely faded.

“Look, the politics of trade have always been complicated,” Obama said in an interview with CNN recorded before his trip to Asia.

Obama noted what he called a “vocal” segment of the Democratic Party, a nod to the popularity of Vermont Sen. Bernie Sanders and the influence of labor union opposition to the deal, as well as the emergence of a new “populist anti-trade sentiment” among some Republicans led by Donald Trump.

But the administration appears unwilling to walk away from the yearslong negotiations with its partners from Asia and the other countries without a final push for the deal.

In addition to potential economic benefits from the deal, Obama sees it as a central element of the U.S. effort to counter China's growing influence in East Asia and the Pacific region.

“The Trans-Pacific Partnership is a historic agreement, cobbled together among a very diverse set of countries, and the basic argument is simple: This is going to be the world's largest market. And if we're not setting the rules out there, somebody else is,” Obama said.

“I remain confident that we can get TPP passed.”

The ambitious trade pact was once viewed as a likely capstone to Obama's second term, a rare chance to find common ground between the two parties, but the election year changed that dynamic.

Even though Congress returns to work this week after its long summer campaign recess, any action in the House or Senate on trade remains nowhere near the top of the agenda. Most lawmakers would prefer to avoid the issue before the November election.

Congress is expected to conduct a post-election lame-duck session, and those final weeks often provide an opportunity for last-ditch legislative maneuvers.

Obama is currently on his final presidential trip to Asia, where he intends to reassure global leaders at the Group of 20 summit that the U.S. is not backing away from its commitment to the continent.

lisa.mascaro@latimes.com