WASHINGTON—Facing uncertain prospects in a series of crucial votes in the House, President Barack Obama made a rare trip to Capitol Hill Friday morning to urge Democrats to stand with him on trade.

A House Democratic aide said Mr. Obama would stop by the House Democratic caucus Friday morning—shortly before lawmakers begin voting on a bill that would grant the president fast-track authority for a Pacific trade deal.

Mr. Obama has launched an unusually aggressive lobbying effort to win his own party’s support for his trade agenda. But with votes quickly approaching Friday morning, the president is still facing razor-thin margins and uncertain prospects. He was counting largely on Republican support to pass trade promotion authority legislation, but was hoping that enough Democrats will vote yes to pass the bill.

As the House of Representatives votes on granting the president trade authority, Obama is heading up against a majority in his own party. WSJ’s Jerry Seib explains. Photo: AP

The president’s excursion to Capitol Hill comes after a surprise appearance Thursday night at the congressional baseball game. There, he made a personal pitch to House Minority Leader Nancy Pelosi (D., Calif.)

The president’s trade agenda rests on a series of contentious House votes in one of the final chapters of a long struggle between the White House and members of the president’s own party.

The House was expected to begin voting late Friday morning on legislation to grant the president fast-track authority for a Pacific trade deal and extend aid to U.S. workers who lose their jobs because of foreign trade. With opposition from both liberal Democrats and conservative Republicans, both measures were expected late Thursday to face close votes as a week of last-minute negotiations wound down.

Passage of the trade legislation would deliver a rare, second-term political gift from a GOP-controlled Congress to Mr. Obama—who squared off against labor groups in a bruising Democratic battle—as well as to business groups and Republican leaders who put aside their suspicion of the White House to advocate for trade.

Approval of fast track would give Mr. Obama the power to submit trade deals to Congress for an up-or-down vote, without amendments, as previous presidents have done. Such power would ease passage of the Trans-Pacific Partnership, a near-final deal between the U.S. and 11 other nations around the Pacific Ocean that would cover nearly 40% of the world economy.

The Senate approved trade legislation late last month, but its fate remained in jeopardy as late as Thursday night in the House, where Democrats raised late concerns over the bill, which many in the party oppose.

“People are worried,” said Rep. Henry Cuellar(D., Texas), one of a handful of Democrats to support the trade legislation. Its opponents have been “brilliant,” he said. “They’ve been trying everything possible.”

In the latest twist, many Democrats were expected to oppose a measure extending a workers’ assistance program long championed by their party. Democrats had balked at a provision in the Senate bill that pays for the program with cuts to Medicare providers.

In a deal painstakingly negotiated and refined this week by Mrs. Pelosi and Speaker John Boehner (R., Ohio), the program, known as Trade Adjustment Assistance, or TAA, would be funded by a different source. But some Democrats still had qualms because the fix would be made through a separate piece of legislation and they worried the structure of the deal could open them up to political attacks over the Medicare cuts.

The House will hold two fast-track votes Friday, one on the portion of the Senate bill that deals with worker aid legislation and—if that passes—one on the part of the bill providing fast-track powers to Mr. Obama. The two issues were split up in a procedural maneuver known as “dividing the question” to allow conservatives opposed to the workers aid to vote against it. The chamber will also vote on altering and passing a customs and enforcement bill already passed by the Senate.

Rep. John Yarmuth (D., Ky.), who on Thursday was leaning against voting for the workers’ aid program, said Democratic concerns over that could derail the full trade package. If the worker-aid portion is defeated, the fast-track vote wouldn’t be held and House leaders would have to regroup.

“It looks to me like there’s going to be a considerable amount of resistance to it among Democrats,” Mr. Yarmuth said. Because the program isn't popular among Republicans, significant Democratic defections could sink it.

Democrats who backed the trade legislation said their workload had now doubled as they scrambled to shore up support for votes on both the fast-track measure and workers’ assistance program.

Rep. Cuellar said that until recently he had only one list of lawmakers to buttonhole on trade—now he has another targeting those wavering on workers’ aid.

“I had one list—now I’ve got two lists,” he said. “We got extra work now.”

Democrats who vote for the trade legislation could face political repercussions heading into next year’s elections.

Jim Dean, chairman of Democracy for America, a progressive political-action committee, warned Democrats against supporting either the workers’ aid program or the fast-track measure.

“We will not lift a finger or raise a penny to protect you when you’re attacked in 2016, we will encourage our progressive allies to join us in leaving you to rot, and we will actively search for opportunities to primary you with a real Democrat,” Mr. Dean said in a statement Friday.

The notion of fast-tracking a trade bill has also met with resistance from conservative Republicans, many of them hesitant to help a president they have clashed with over health care, immigration and other issues.

House Ways and Means Committee Chairman Paul Ryan (R. Wis.), an influential conservative, has put much of his own political capital on the line as he has sought to build support for the trade legislation.

“A yes vote would be a huge win for conservatives, free-market principles and American leadership,” Mr. Ryan wrote in an editorial published late Thursday in the Washington Examiner. “Many of the president’s critics are rightly concerned that he too often keeps Congress in the dark. But [the fast-track measure] will turn on the lights.”

Passage of both measures would send fast-track legislation straight to Mr. Obama’s desk, ending the uncertain congressional support that is seen as crucial to completing the Pacific trade deal.

If fast track becomes law, the trading partners—including Japan and Vietnam—could wrap up the TPP in coming weeks. Still, complicated bureaucratic requirements mean the TPP is unlikely to come to a final up-or-down vote in Congress before the end of the year, and could come well into next year.

Even if fast track passes, the later fight on the Pacific trade deal could turn out to be longer and more politically divisive if it occurs in the spotlight of the 2016 election cycle, officials and trade experts say. Besides the TPP, the fast-track legislation could expedite potential trade deals with the European Union and other trading partners for the next six years.

Failure of the trade legislation Friday would mark a decisive victory for unions, who launched an aggressive campaign to defeat the legislation in final weeks, including releasing ads attacking individual lawmakers and threatening to take revenge in future elections.

To counter that, Mr. Obama has indicated he will lend his support to lawmakers who backed him on trade.

Rep. Scott Peters (D., Calif.), who Thursday hadn’t decided yet how he would vote, said Mr. Obama had called him two or three times to discuss the topic.

“He’s generally said that he’ll have the back of people who support him on this so I’ll find out what that means if I vote yes,” said Mr. Peters. “It’s a tough vote for me because my district’s very trade-dependent, but there’s a lot of fear about what happens if we vote for TPA.”

—Siobhan Hughes, Colleen McCain Nelson and Melanie Trottman contributed to this article.

http://www.wsj.com/articles/obamas-trade-agenda-faces-crucial-votes-in-house-1434101402