House Minority Leader Nancy Pelosi (D-Calif.) says she has told Speaker John A. Boehner (R-Ohio), that it will be up to him to rally Republicans to pass President Obama’s trade promotion bill in the House. (Michael Reynolds/European Pressphoto Agency)

President Obama opened an intense final round of lobbying to win support for his sweeping Pacific Rim trade accord ahead of a crucial vote in the House as soon as next week, expressing confidence that he will overcome deepening skepticism among fellow Democrats.

The push from the president included direct calls to lawmakers, interviews with television stations in key states and plans to bring several Democrats aboard Air Force One with him to a summit in Germany this weekend. Obama is asking them to support legislation, approved by the Senate last month, that would grant him fast-track authority to complete the Trans-Pacific Partnership (TPP), a 12-nation pact that the president has called central to his second-term agenda.

In a sign of how high the stakes have become, the White House was coordinating its efforts with House Republican leaders, who are in rare agreement with Obama and are canvassing for as many votes as possible from their caucus to ensure a buffer if the president is unable to win much support from his party.

Their challenge remains daunting, though. Minority Leader Nancy Pelosi (D-Calif.) on Thursday promised no more than 18 votes from the 188 House Democrats — well below the two dozen or so that the administration has been seeking. That would mean Republicans would have to deliver at least 200 votes in favor of the bill.

House Speaker John A. Boehner (R-Ohio), who declined to disclose his vote tally Thursday, said that he talked by phone to Obama a day earlier. “He’s got some work to do,” Boehner said of Obama. Boehner warned that if the votes do not materialize this month, the administration’s trade agenda is probably doomed.

White House aides foisted the pressure back onto Boehner, noting that the House GOP won a larger majority during the midterm elections in the fall and that the speaker has promised to move his agenda through the chamber.

“I never hypothesize that we’re not going to get this done,” Obama told a Seattle TV station. “I’m pretty confident we’re going to be able to get this done.”

The fight over the accord has placed Obama in opposition to most Democratic lawmakers at a time when the party is trying to coalesce ahead of the 2016 race for the White House. Some Democratic presidential primary candidates, including Sen. Bernie Sanders (I-Vt.) and former Maryland governor Martin O’Malley, have denounced the deal, while former secretary of state Hillary Rodham Clinton has hedged on whether she would support it.

The president’s trade initiative has faced fierce opposition from labor unions, environmental groups and Capitol Hill progressives, which fear that the TPP would lead to job losses and harm the economy. Opponents delivered a petition to lawmakers Wednesday with what they said were 2 million signatures opposing the fast-track bill.

The president granted a round of interviews to TV stations in Texas, California and Washington state in a bid to provide political cover to wavering lawmakers in states that rely heavily on foreign trade. In recent weeks, Obama has personally promised Democrats who back his trade initiative that he would campaign for them against any primary challengers.

Obama got a boost this week when Rep. Jim Himes (D-Conn.), long considered one of the most pro-trade Democrats in Congress, finally announced his support.

“I’ve probably heard the word ‘disappointed’ a thousand times in the last 24 hours” from labor and environmental groups, Himes said. “On the other hand, there’s been a lot of support from people I consider thoughtful, careful observers.”

Among the television stations Obama appeared on was one in El Paso, home to Rep. Beto O’Rourke (D-Tex.), who remains undecided. Anti-TPP protesters rallied outside his office there just before the interview with Obama aired Wednesday evening.

“It helps insofar as the community gets to hear directly from the president, but it’s not going to push me one way or the other,” O’Rourke said Thursday in Washington.

Asked what his vote will come down to, he said: “It’s making sure this is the right thing for the country and my community. . . . We potentially have a lot to gain in this, but I want to make sure that that is in fact the case.”

For Obama, there remains tough resistance to the deal from the Congressional Black Caucus, a key constituency of the president’s. Some members have been responsive to White House arguments that Obama has faced more opposition in getting basic powers that other presidents have had. President George W. Bush enjoyed fast-track trade authority from Congress from 2002 to 2007, for instance.

But many black lawmakers dismiss any race-based allegiance to Obama on this issue. “So what? [Conservative Supreme Court Justice] Clarence Thomas is black. That doesn’t mean much to me,” Rep. Cedric L. Richmond (D-La.) said in an interview, adding that he doubts this trade deal will benefit his largely minority district.

In another interview with a Sacramento television station Wednesday, Obama offered direct support for Rep. Ami Bera ­(D-Calif.), who, since declaring his support for fast-track trade legislation, has been vehemently denounced by labor unions.

“The truth of the matter is he’s doing the right thing,” Obama said of Bera. Although the president referred to himself as a “brother-in-arms” with organized labor over efforts to raise wages, he challenged labor leaders to explain why they do not want to rewrite global rules if they think the United States has been harmed by past trade deals.

“They typically don’t have a great answer for that,” Obama said.

On the House Republican side, the whip team is working with Rep. Paul Ryan (R-Wis.), chairman of the Ways and Means Committee, to win over blocs of votes at a time, sometimes focusing on specific states where three or four members from the same delegation might vote together.

GOP aides have expressed optimism, but they continued to face problems, not just among the far-right group of conservatives who have caused so much trouble for Boehner in the past. With their gains in two of the past three elections, Republicans now hold many seats that lean toward Democrats, such as the Long Island district of freshman Rep. Lee Zeldin (R-N.Y.).

He has faced protests from liberal groups in his district all spring. On Thursday, the American Action Network, a super PAC affiliated with Republican leadership, announced that it launched a mail and online ad campaign promoting the trade deals in Zeldin’s district, as well as 64 others.

Obama also appeared on the public radio show “Marketplace,” where he acknowledged that some sectors of the U.S. economy will be harmed by the Pacific trade accord. But he vowed that the benefits of the pact would far outweigh the costs.

“The question is, ‘Are there a lot more winners than losers?’ ” Obama said. “And the answer in this case is yes.”

Mike DeBonis contributed to this report.