President Obama pushes his trade agenda at Nike headquarters in Beaverton, Ore., on May 8, 2015. (Jonathan Ernst/Reuters)

The Senate barreled toward a cliffhanger on trade Tuesday in the face of serious Democratic opposition to legislation that would allow President Obama special authority to close global trade deals.

The Democratic infighting left Obama’s highly sought “fast track” authority in political limbo, with opponents believing they have the votes to block the measure. Such a move would create the unusual possibility that the president’s own party would launch a filibuster against his coveted trade agenda.

Obama and his Cabinet officials have mounted a furious final effort to lock up the votes in both chambers to secure the “Trade Promotion Authority” and then move on to wrapping up the final details of a trade agreement with 12 Pacific-rim nations.

“He’s made a very strong case about why he believes that this is the best interest of our economy both in the short term and over the long term,” White House press secretary Josh Earnest said Monday.

With a few Republicans expected to oppose the TPA legislation, Obama will need roughly 10 Democrats to join about 50 Republicans to clear a 60-vote hurdle on a filibuster vote Tuesday afternoon to move forward with the fast-track legislation.

The new authority would set up a faster process for congressional consideration of future trade deals, forcing an up-or-down vote without giving lawmakers the ability to amend the deal. Obama, similar to previous Republican and Democratic presidents, views having this authority as key to finalizing global trade deals, arguing that it would make negotiating with multiple nations virtually impossible if each country’s legislature was able to tinker with the agreement.

The debate has turned increasingly heated between Obama and his normally supportive base of anti-Wall Street progressives, particularly Sen. Elizabeth Warren (D-Mass.).

Warren returned fire Monday in an interview with The Washington Post’s Plum Line blog, accusing the president and his advisers of trying to “grease the skids” for a deal while he “won’t actually let people read the agreement.”

“If the president is so confident it’s a good deal, he should declassify the text and let people see it before asking Congress to tie its hands on fixing it,” she said.

That came after Obama, during a stop at Nike’s Oregon headquarters promoting trade, gave a searing assessment of Warren’s critique on the trade packages he is negotiating. In an interview with Yahoo News, he labeled her a “politician like everybody else” who is “absolutely wrong” when she says the emerging Trans-Pacific Partnership would create a path for a future Congress to undermine the Dodd-Frank overhaul of Wall Street regulations.

On Monday, Earnest stepped up the criticism by accusing Warren of distorting the argument on transparency, noting that any member of Congress can review the current details of the Pacific trade deal in a secure room in the Capitol basement.

“If Senator Warren is wondering what she’s voting on, then she can walk over to the room that has been established on Capitol Hill by the U.S. trade representative and she can read the latest version of the negotiated document. So there is no need for this false criticism,” Earnest said.

Senate passage was once considered a sure thing for TPA and the Pacific trade deal, with White House officials hoping that a large bipartisan majority would support the fast-track legislation and provide a springboard for what was expected to be a much narrower path to victory in the House.

The vast majority of the 245 House Republicans are expected to support the president, leaving White House officials to find possibly 25 to 30 Democratic votes. According to one Democratic estimate provided Monday, there are just 17 House Democrats so far supporting TPA.

But now the Senate outcome is up in the air amid last-minute complaints from some Democrats demanding a side package of concessions.

Sen. Ron Wyden (D-Ore.), the top Democrat on the Senate Finance Committee who negotiated the details of the fast-track trade bill, has told his colleagues that he will not support starting the debate unless several bills designed to help protect U.S. workers are given assurances that they would become law at essentially the same time, according to senators and advisers to Wyden.

Republicans have so far signaled a willingness to include only one extra bill, creating federal support for labor retraining if workers can prove they have lost a job because of foreign competition.

Democrats are keenly interested in approving a bill that largely deals with U.S. customs issues but includes language that would crack down on alleged currency ma­nipu­la­tion by Chinese officials who want to make their products cheaper on the global markets. It also includes stronger enforcement measures to determine whether nations are cheating on their promises.

Senate Majority Leader Mitch McConnell (R-Ky.), who has offered unusual praise for Obama’s efforts on trade for several weeks now, criticized Wyden and other Democrats for impeding their party’s president in a way that would not even allow debate to begin on his legislation if they succeed Tuesday.

“Some talk about preventing the Senate from even debating the bill. I would tell you, I think that would be a big mistake,” McConnell said during a Senate floor speech Monday, noting that these Democrats are blocking Obama’s agenda. “This bill is indeed worthy of debate by the president of the United States.”

Minority Whip Richard J. Durbin (D-Ill.) said he had “no indication” that Republican leaders would agree to combine the various bills in such a way that would pass muster with enough Democrats to proceed.

“I would say, at this point, most Democrats are inclined to vote no unless they know what they’re voting for,” he said.

The most important piece, he said, was the enforcement legislation that carries provisions addressing, among other things, currency manipulation.

“The question is, what is going to happen to this bill?” Durbin said. “Is it going to come separately? Is it going to be guaranteed a vote in the House? Is the president inclined to sign it if it comes to his desk? Those are all pretty important questions that a lot of people would like to know the answer to.”

Mike DeBonis contributed to this report.