People hold signs opposing the Trans-Pacific Partnership at the Democratic National Convention last week in Philadelphia. (Mandel Ngan/AFP/Getty Images)

President Obama will use a visit from the prime minister of Singapore on Tuesday to launch a final public campaign for a landmark Asia-Pacific trade accord, but proponents are losing hope that the deal can survive the strong anti-trade rancor among fellow Democrats.

Presidential nominee Hillary Clinton forcefully reiterated her opposition to the Trans-Pacific Partnership at the Democratic National Convention last week, a move intended to quell unrest among party liberals but an outcome that White House allies saw as a setback for the administration.

Administration officials said Obama intends to reassure Singapore’s Lee Hsien Loong during a White House meeting that Congress will ratify the TPP before the president leaves office in January. But that is looking increasingly less likely.

The White House is eyeing what is expected to be a brief lame-duck session of Congress after the Nov. 8 elections as the final window, and even then the politics will be fraught. Last month, Senate Majority Leader Mitch McConnell (R-Ky.) called chances for the deal “pretty slim” this year.

With time running out, Obama on Monday reaffirmed his commitment to the 12-nation deal and declared that he remains optimistic that Congress will ultimately support it.

“I know that the politics around trade can be very difficult, especially in an election year,” Obama said in a written interview with the Straits Times of Singapore.

Acknowledging the changes wrought by globalization for American workers, the president added: “The answer isn’t to turn inward and embrace protectionism. We can’t just walk away from trade. In a global economy where our economies and supply chains are deeply integrated, it’s not even possible.”

In an interview with The Washington Post, Lee said the demise of the TPP would amount to “unmitigated bad news” for the United States. He suggested the nation’s prestige and leadership in Asia is at stake given China’s growing influence in the region.

“The question is what America will do in that landscape,” Lee said. “One big thing you have done is TPP. ... Now if you say, ‘No, we don’t believe in such trade agreements anymore,’ everyone around the region will have to recalculate.”

Obama’s campaign for the TPP over the next few months, including making the case on a trip to Asia in September, will put him squarely at odds with Clinton. Her campaign moved last week to squelch a furor over remarks from a surrogate, Virginia Gov. Terry McAuliffe (D), who suggested Clinton would drop her opposition to the deal after the election. Clinton supported the TPP while serving as secretary of state in Obama’s first term.

“I can be definitive. She is against it before the election and after the election,” Clinton campaign chairman John Podesta said last week.

The unambiguous denunciation alarmed proponents who had hoped that Clinton’s move to the left on trade during a hard-fought primary campaign against Sen. Bernie Sanders of Vermont would soften during the general election.

Instead, Clinton has reaffirmed her opposition as she moves to consolidate Sanders’s supporters and protect against attacks from Republican nominee Donald Trump, who has bucked GOP orthodoxy on trade and also opposes the TPP.

“The administration outwardly remains optimistic,” said Miriam Sapiro, who served as the acting U.S. trade representative in 2013. “But I sense more realism is creeping in. My view is that it’s getting harder each day.”

White House aides suggested the widespread anti-TPP rhetoric at the Democratic convention did not reflect the party’s overall views on trade. An NBC News-Wall Street Journal poll in July found that 60 percent of Democrats and 51 percent of Republicans support free trade and believe opening foreign markets is good for the U.S. economy.

Administration officials also have said the small but important Democratic coalition in Congress that helped pass a bill last summer granting Obama greater trade powers remains committed to the TPP.

But the White House has struggled to convince the public of the economic benefits of the trade pact, which is composed of nations that make up 36 percent of the world’s gross domestic product, including Japan, Mexico, Canada, Australia, Malaysia and Vietnam. The sprawling pact addresses tariff reductions for agriculture and automobiles, as well as intellectual-property rights for movies and pharmaceutical drugs, the free flow of information on the Internet, wildlife conservation, online commerce and dispute settlement practices for multinational corporations.

A study by the U.S. International Trade Commission said the TPP would have a marginal impact on the U.S. economy, adding $43 billion in 15 years and creating an estimated 128,000 jobs.

Obama’s meeting with Lee, which will feature a White House state dinner, offers an opportunity for the president to tout the geopolitical benefits of the TPP. Singapore, a tiny island nation, is a Southeast Asian hub with an economy largely built around free trade.

Singapore was one of four countries — with New Zealand, Chile and Brunei — that began talks in 2005 for a regional free-trade pact that ultimately grew into the TPP. Obama announced in 2011, during an Asia-Pacific economic summit in Hawaii, that his administration would take a leading role in the accord.

The White House has said the trade deal offers a bulwark against China, which is pitching its own regional trade pact in Asia. U.S. officials said the Chinese proposal does not address labor, environmental and human rights protections that are included in the TPP.

In an address in Singapore in November 2012, Clinton predicted the TPP would help raise working standards and create better jobs. In the interview, Lee said Clinton’s reversal would put her in a difficult bind if she wants to revisit the pact as president.

“A position taken in an election cannot be lightly unspoken,” he said.

Retired Adm. Mike Mullen, a former chairman of the Joint Chiefs of Staff, said the trade accord is a crucial strategic initiative to build partnerships in Asia that could reduce conflicts and maintain national security. In an interview, Mullen added that if lawmakers fail to ratify the deal, it could be another decade before the United States musters the political will to get it done.

The TPP “involves parts of the world that I’ve said for a decade are at the center of the economic universe for the 21st century,” Mullen said.

But Democratic opponents of the TPP, including Sanders and Sen. Elizabeth Warren (Mass.), have characterized the accord as a boon for corporations at the expense of American workers.

Scores of Sanders supporters carried anti-TPP signs inside Wells Fargo Center during the Democratic convention in Philadelphia last week.

“Maybe someone in the White House saw it coming, but many people who have followed this closely are surprised by how explicit the anti-TPP sentiment has been,” said David Adelman, a proponent of the pact and partner in the law firm Reed Smith who served as the U.S. ambassador to Singapore from 2010 to 2013.

“People are still talking about the lame-duck session,” Adelman said. “But the politics on the presidential campaign trail would seem to make it very difficult for there to be enough votes. There’s so much heat, much more than anyone predicted.”