The TPP is a proposed free trade zone comprising 12 countries on both sides of the Pacific Ocean: the US, Japan, Malaysia, Vietnam, Singapore, Brunei, Australia, New Zealand, Canada, Mexico, Chile and Peru.
Described as "a sort of NATO-on-trade that excludes China," the stated aim of TPP is to increase trade by removing import tariffs within the free trade zone.
However, labor groups in the US and other developed countries in the proposed zone have expressed concern that it could lead to jobs leaving for other TPP members with lower wages and looser labor laws. The GDP per capita in the poorest TTP country, Vietnam (1,910 USD per year in 2013, according to the World Bank) is a fraction of that in Mexico, Malaysia or Peru, let alone the US, Canada, Australia or New Zealand.
Like the Transatlantic Trade and Investment Partnership (TTIP) currently being negotiated with the EU, the TPP is also criticized because of the secrecy of its negotiations.
In an article for the US magazine Foreign Policy, Stavridis wrote that failure to pass the deal would lead to a loss of US influence in the crucial Asia-Pacific region, to the benefit of China.
"The American Brexit is coming," warned Stavridis, who thinks rejection of the deal would be "a colossal mistake."
"It was a serious geopolitical mistake for Britain to walk away from the European Union, and it would be equally serious for the United States to leave the TPP on the table and effectively walk away from a leadership position in Asia," Stavridis, a former NATO supreme allied commander, wrote.
"China clearly intends to be the dominant actor in East Asia, and absent a strong US presence, it will succeed."
Several recent events have caused Stavridis to worry about Washington's standing in the Pacific region. President Rodrigo Duterte of the Philippines, a traditional US ally, is talking about increasing ties with China. China is increasing its activities in the South China Sea and around the disputed Senkaku (Diaoyudao) Islands, which are controlled by US ally Japan.
"A nation's influence is the composition of its military, cultural, political, and — above all — economic influence. As the leader of what would be the largest free-trade zone in the world, the United States would continue to exert real leadership in this crucial region."
US President Barack Obama is desperate to have the Senate ratify the agreement before the end of his presidency, which would bolster the "pivot to Asia" foreign policy for which the President has little to show.
However, in August US Senate leader Mitch McConnell said that the Senate will not vote on the legislation this year, because the deal in its current form "has some serious flaws."
That leaves TPP in the hands of the next president, and the presidential candidates from both parties appear skeptical about the agreement.
Democratic candidate Hillary Clinton once called TPP "a cutting-edge, next generation trade deal," and the "gold standard of trade deals," but has since moved her position closer to Republican rival Donald Trump.
"I did say I hoped it would be a good deal. I was against it once it was finally negotiated and the terms were laid out," Clinton said in a debate with Trump last week, when the Republican brought up her U-turn.
In contrast, Trump has consistently spoken out against the treaty on the basis that it would lead to the loss of American jobs.
"American manufacturing is being led to the slaughter," he told a rally last month.
"A vote for Hillary Clinton is a vote for TPP and the continued destruction of America's jobs."
Trump wants to follow a more isolationist foreign policy, and warned that "I don't want to be taken advantage of," by NATO countries which don't pay "their fair share" of financial contributions to the alliance defense budget.
"We're protecting countries that most of the people in this room have never even heard of and we end up in world war three … Give me a break," Trump told a rally in Pennsylvania in July.