By Siobhan Hughes And Gerald F. Seib 

President Barack Obama escalated a public feud over international trade with the liberal wing of his own party, a brawl that threatens to undermine one of the key goals for the White House this year.

The schism over trade widened with several testy exchanges this week between Mr. Obama and his liberal base, including remarks Friday in which the president said critics were mischaracterizing the deal.

At the heart of the fight is the 12-nation Trans-Pacific Partnership trade deal and the push in Congress to approve "fast track" legislation to expedite passage of the deal later this year. But the tussle touches on longstanding divisions over trade among Democrats.

In an attempt to assuage critics, Mr. Obama said Friday that the Pacific deal wouldn't repeat what he called the mistakes of earlier trade deals, particularly the 1994 North American Free Trade agreement between Mexico and Canada that was championed by President Bill Clinton and passed with more Republican than Democratic votes in Congress.

"When I listen to critics of this deal--and they are friends of mine--what I primarily hear are criticisms of Nafta," Mr. Obama said, promising that the Pacific pact "will end up being the most progressive trade agreement in our history."

The president's struggles to win over traditional allies have been particularly vivid in his interactions with lawmakers from the Congressional Black Caucus, which numbers 42 Democrats in the House. As with many other Democrats, caucus members focus on the fear of job losses in their districts.

"I'm with him on probably just about everything," said Rep. Joyce Beatty (D., Ohio), who noted "a greater responsibility to my constituency" to explain why she was leaning against the president on trade.

Nearly all top Democrats in the House and Senate, as well as a number of prominent liberals, such as Sen. Elizabeth Warren of Massachusetts, have expressed skepticism or outright opposition to the fast-track legislation in recent days. Many are also opposed to further opening trade with Pacific trade partners.

Even Hillary Clinton, who promoted the Pacific deal during her four years as Mr. Obama's secretary of state, now hasn't taken a position on the pact, saying she wants to see the details of how it will protect jobs and advance American interests.

Complex trade deals are traditionally negotiated in secret, with their voluminous details released only upon completion.

Still, Ms. Warren and other Democratic critics have accused the administration of a lack of transparency in negotiating the Pacific pact with Japan, Australia, Chile, Vietnam and eight other countries. "The government doesn't want you to read this massive new trade agreement," Sen. Warren wrote in a letter Wednesday to supporters. "It's top secret."

Mr. Obama's attacks on the liberal wing of the Democratic base have gotten increasingly pointed as he has sought to blunt the impact of the strong liberal pushback against the trade deal. The first shot came Tuesday, when Mr. Obama said in a MSNBC interview that critics on the left "don't know what they're talking about," and labeled Ms. Warren as "wrong on this."

The president escalated the battle on Thursday in remarks to Organizing for Action, a nonprofit that grew out of his presidential campaign organization, when he urged critics to "look at the facts--don't just throw a bunch of stuff out there and see if it sticks."

He even compared liberal critics to former Alaska Republican Gov. Sarah Palin, saying their opposition was similar to her assertion that his overhaul of the health-care industry would include "death panels."

Progressives have taken umbrage, and say Mr. Obama's argument would be stronger if he publicly released the negotiating text that will form the basis of the 12-nation trade deal.

"American workers who have lost their jobs due to trade deals are understandably skeptical," said Eric Hauser, communications director for the AFL-CIO, the labor federation that includes millions of workers, in a statement. "The best way to regain workers' confidence is to release the text, not scold the critics," he said.

As Mr. Obama seeks to win over supporters for his trade agenda, the math looks particularly tight in the House. Lawmakers must first pass a fast-track bill, which would open the way for the Pacific deal by ensuring it would go to Congress for an up or down vote, without amendments.

The Senate Finance Committee passed the fast-track bill this week with overwhelming support, paving a path to the floor as early as next week. The timing of a House floor vote was uncertain after the House Ways and Means Committee passed the same measure with the support of only two Democrats.

To make up for what could be dozens of Republican No votes in the House, the administration may need to persuade 20 or more House Democrats to vote Yes. The White House hopes some of those votes will come from members of the black caucus. But the going has not been easy.

Rep. Yvette Clarke of Brooklyn is a loyal Obama supporter, but she found she couldn't say yes earlier this month when the president engaged in some personal lobbying.

Traveling on Air Force One on a trip to Jamaica, the president sat down with Ms. Clarke and made the case that failure to pass the Pacific trade deal would erode U.S. leverage and give a leg up to China.

Ms. Clarke promised to "go back and have a conversation with my constituents," she said, recounting the conversation. But she isn't optimistic: "The people in my district--they are radically against" the Pacific trade deal, Ms. Clarke said in an interview.

Earlier this year, it seemed the caucus might be a productive target, even though it had opposed Mr. Obama several years ago when he won passage of pacts with South Korea, Colombia and Panama. After a meeting in February between Mr. Obama and the caucus, the group's leading voice on trade, Rep. Charlie Rangel (D., N.Y.), emerged optimistic that an agreement that would satisfy both sides was within reach.

"If they can make the trade bill look like a jobs bill, then there's no problem," Mr. Rangel said he told the president, predicting in a February interview that "somebody is going to be drinking champagne when this thing is over."

But by last week, Mr. Rangel sounded pessimistic about finding common ground with the Obama administration. He said the White House hadn't offered him anything concrete that would assure jobs--at least "nothing that I could explain to my voters."

Two-thirds of the House members in the caucus signed a letter to Mr. Obama complaining that any trade deal would need to do more to strengthen workers' rights. And only Rep. Gregory Meeks (D., N.Y.) is on record in favor of the fast-track legislation, and Rep. Eddie Bernice Johnson (D., Texas) is thought to be a swing vote.

"There's too much downward pressure on wages," said Rep. David Scott (D., Ga.), a frequent ally of businesses who said he has made clear that the White House shouldn't even bother trying to win his vote.

On the call Friday, Mr. Obama said he was "not ideologically wedded to free trade for free trade's sake." Upon entering office, he said, "I was very clear about the need for us to change the way we do business" on trade matters.

But of the Pacific agreement, he said, "I am confident that American workers will win."