The biggest beneficiary of the United States' inability to reach a consensus with its trading partners on the 12-nation Trans-Pacific Partnership may be Democratic presidential candidate Bernie Sanders, a staunch critic of President Obama's trade agenda.

The Obama administration had hoped to wrap up the remaining details during a meeting in Hawaii over the weekend. But lingering disputes over issues ranging from automobiles, to dairy, to rice to pharmaceutical patents could not be resolved.

As a consequence, a vote in Congress isn't likely until January or February at the earliest, traditionally the height of the Democratic primary season. This will be a unique opportunity for Sanders, a sitting U.S. senator from Vermont.

"Bernie will help lead the [Senate] opposition," said Robert Borosage, co-director of the Campaign for America's Future, a liberal activist group. That will boost him among liberal activists at a crucial point in the primary.

At the same time, Borosage noted, it will be a problem for Hillary Clinton, who has tried to remain above the trade fight by not taking a firm position.

"Hillary would be forced to take a position, once she saw the text. Unclear where she would come down, although I suspect she'll end up favoring it," he said.

Ken Zinn, spokesman for National Nurses United, a union coalition fighting the trade deal, agreed that the timing would be "extremely difficult" for Hillary Clinton. "She keeps saying she wants to see the final deal before she makes a decision. This way, she won't be able to avoid taking a position," he said.

If she opposes the deal, she will risk looking disloyal to Obama and alienating his fans. If she supports it, she will have to fend off charges of being Wall Street's candidate.

Both said the timing was so tricky they wouldn't be surprised if the vote is pushed further back into 2016 just to get it clear of the primaries. But that itself would be a problem for the administration, which is eager to get the deal done and doesn't want to risk any further delays.

The tension was on display last week when both Clinton and Sanders, among other candidates, met privately with the AFL-CIO labor federation's executive board, a major part of the Democratic Party's coalition. It is also staunchly opposed to the trade deal.

Clinton refused to take a position on the deal, she told reporters afterwards. Sanders had no such reticence. The board, which includes friends and allies of Clinton, subsequently said that it would make no endorsement at that time.

An administration source involved in the trade negotiations who requested anonymity conceded it had handed a potential soapbox to Sanders but argued that it wouldn't make much of a difference.

Getting Trade Promotion Authority passed was the harder fight, the source said, since the legislation was about the congressional process and not the contents of any actual deal. The Pacific Rim deal will likely be easier since the administration will be able to point to specific gains from the deal.

The source added that Sanders would just be one voice and noted that trade critics such as Sen. Elizabeth Warren, D-Mass., and Rep. Rosa DeLauro, D-N.Y., had been more prominent in the previous fights.

One thing all sides agreed on was that an early 2016 vote was the optimistic scenario for the administration. There is no guarantee that the remaining disputes over the trade deal will be ironed out in the coming weeks, meaning Congress may not vote until mid-2016 or even later.

In addition, the Republican leadership will control the timing of the vote. The GOP leaders are expected to support the pact as they did Trade Promotion Authority, but it remains a factor outside the administration's control.

"Remember, this is up-down vote, no amendments, no filibuster. So if [Senate Majority Leader Mitch] McConnell, R-Ky., and [House Speaker John] Boehner, R-Ohio, chose, the vote could occur rapidly," Borosage said.

But he argued it was "not at all clear" what they would do in an election year and that past proposed trade deals had ended up being handed off from one administration to another.

President Bill Clinton completed the North American Free Trade Agreement, a deal that President George H.W. Bush negotiated, as it was put off in election year. Obama himself signed a deal with South Korea that President George W. Bush had negotiated.