WASHINGTON » On the evening of June 15, President Barack Obama joined a conference call with the two men who had done more than anyone in six years to disrupt, derail or defeat his agenda in Congress. Now they were asking for something that was in short supply: trust.

The president was nervous about their plan, but he desperately needed their help. Most of Obama’s own party had deserted him on a critical trade vote three days earlier, hours after he had begged them not to. And the Democratic leaders in both chambers were bitterly opposed to his plans to cooperate with Republicans on a far-reaching trade pact with Pacific Rim nations.

Sen. Mitch McConnell, the majority leader, bluntly laid out his plans to save the president’s trade push, and House Speaker John Boehner endorsed it on the call. It would be up to Obama, the two Republicans said, to deliver a handful of Democrats in each chamber for a new set of trade votes — a high-stakes test for a president who has often seemed indifferent to legislative arm-twisting and whose relationships with lawmakers, even in his own party, have frequently been questioned.

"I said, ‘Mr. President, all you have to do is get the same 28 Democrats in the House who voted for it once to do it again,’" McConnell said in an interview this week. And, he told the president, "get the 14 Senate Democrats" too.

Obama made no firm commitments to the Republicans on the call, according to White House aides, though he warned McConnell and Boehner they would have to come up with some additional measures to "sweeten the pot" for his pro-trade Democrats. If the trade vote failed a second time, the broader agreement among 12 Pacific nations could die along with it.

The plan worked. On Thursday, the House voted on the final piece of trade legislation Obama needed to clear the way to a legacy-defining pact linking 40 percent of the global economy into a complex web of rules, from lower tariffs to intellectual property protections to expanded Internet access.

In the end, all it took was McConnell’s parliamentary acumen and creativity, the president’s nonstop pleading and House Democratic maneuvers that at first blush looked like tactical brilliance but proved too clever by half.

The Campaign

The campaign to lock in those Democrats began more than a year ago. Michael B. Froman, the president’s top trade official, members of the Cabinet and senior White House staff members targeted about three dozen lawmakers, their names collected in binders and listed in Excel spreadsheets and on dry-erase boards. They called into local radio programs and TV stations, took members to lunches and visited their districts to meet with dairy farmers or environmental groups.

Officials knew there would be few Democrats open to a trade deal. Since 1979, a Democratic president had not pushed through fast-track authority, which provides international trade deals an up-or-down vote in Congress without amendment or filibuster. With many Democrats suspicious any trade deal would be a giveaway to big corporations that could lead to substantial job losses among American workers, the administration would be lucky to get more than a handful.

And there was additional pressure from unions and environmental groups who opposed the trade pact and were threatening Democrats who voted for it. At one Democratic caucus meeting, Rep. Peter A. DeFazio of Oregon, an opponent of the deal, lashed out at Froman.

"The politest thing to say is he is dissembling or outright lying," DeFazio said later, a charge Froman attributes to misinformation from the opposition groups.

On the second floor of the West Wing, a "war room" became a second home to people like Froman; Jeff Zients, director of the National Economic Council; Labor Secretary Thomas E. Perez; and Commerce Secretary Penny Pritzker. Slowly, they had assembled 28 pro-trade Democrats in the House and 14 in the Senate, though one of them would drop away. The Senate had passed the trade authority bill, and a worker assistance measure.

By June 12, White House officials believed they had succeeded.

As the critical vote approached that day in the House, Obama made an unscheduled dash to the Capitol to try to persuade fellow Democrats to "play it straight." But that morning, Rep. Nancy Pelosi of California, the Democratic leader in the House, told the president she would try to block trade authority by holding up the worker assistance bill.

Initially, Boehner had planned to cancel a vote on the trade authority if the worker assistance measure failed. But as it became apparent what Pelosi was planning, Boehner and his chief of staff, Michael Sommers, had a change of heart.

"Why wouldn’t we lock this down and show that we’ve got the votes?" Boehner recalled in an interview. "So we changed our mind. It was a key moment."

The trade authority measure narrowly passed, but Pelosi succeeded in killing the worker assistance bill, knowing that without a victory on both bills, everything stalled for Obama and the Republicans. At the White House, "it was not elation," one official recalled. Among Republicans, "they were crying into their coffee," as one senior aide put it.

House Republicans took to the microphones to declare the fight not over. Josh Earnest, the White House press secretary, struggled to express optimism, calling the stumble in the House just another example of a "legislative snafu" that — somehow — would be corrected.

"Figuring out the legislative procedure and the path forward will principally be the responsibility of members of the legislature," Earnest said.

The Path Forward

Over the weekend, Boehner and McConnell tried to do just that. But it wasn’t immediately obvious what the path might be.

Simply trying to force another House vote on the workers’ measure would mean hoping that dozens of lawmakers in both parties would suddenly change their votes, a highly unlikely situation — even if that was the preferred option of the White House. In the end, the Republican leaders decided to move the fight back to the Senate, where they would hold two separate votes again — one on trade authority and another on the worker assistance bill.

Because the House vote on trade authority, called TPA, passed, there was an opening. McConnell just needed to find the right parliamentary magic to get it passed in the Senate and sent to the president.

"That’s what opened the door, the fact that the votes were there for TPA," McConnell said. "That was helpful, because the whole approach I came up with relied on simply replicating that vote, one more time."

The key was trust. Democrats who supported the trade deal were being asked to vote for trade authority without worker retraining assistance attached, on Republican leaders’ word they would help pass the worker assistance measure shortly after.

McConnell first took advantage of a blunder Pelosi had made earlier in the process. By demanding a new way to pay for the worker assistance, she had forced House Republican leaders to amend a popular African trade initiative, sending it back to the Senate for another vote — and giving McConnell the bill he needed to save the trade push.

McConnell’s parliamentary experts added the worker assistance bill to the African Growth and Opportunity Act, a bill almost certain to earn bipartisan support in both chambers. That provided Democrats who wanted the trade deal with some assurance McConnell would make good on his promise to pass the measure.

Members of the Congressional Black Caucus, who disliked opening the door to a trade deal but were champions of the African measure, were particularly torn.

"I’m angry and disgusted to be put in this situation," declared Rep. Keith Ellison, D-Minn. Still, they had little choice but to support the combined bill.

McConnell added a sweetener to make the deal more palatable, a measure that would speed up the government response when foreign competitors "dump" products like steel on U.S. markets at artificially low prices. That attracted Rust Belt lawmakers in both parties.

Boehner and McConnell issued a joint statement declaring they would work to pass the worker assistance bill. At the same time, Obama worked the phones personally on June 16, calling 10 of the pro-trade senators, some from the White House residence late into the night.

"They needed many more assurances," one administration official said.

Among them was Sen. Ron Wyden of Oregon, the ranking Democrat on the Senate Finance Committee, who was among the leaders pushing for the trade authority. When Denis McDonough, the White House chief of staff, had called him on Father’s Day, Wyden insisted his coalition would not abandon the worker assistance measure, known as TAA in Washington jargon.

"Our message was, ‘We’re not trading TAA for TPA,’" Wyden said. "TAA is vital for workers and has been since the Kennedy days of the 1960s."

But soon, Democratic support for McConnell’s approach grew.

On Wednesday, June 17, before hosting members of Congress at the annual White House summer picnic, Obama met separately with the pro-trade Democrats in the House and Senate. With the votes looming again, the group seemed solid: 13 in the Senate and 28 in the House. No one had wavered.

The Senate voted Wednesday to pass both measures — the trade authority bill and the worker assistance measure. A final vote on the worker bill in the House on Thursday completed the complex legislative maneuver, sending both bills to the president for his signature.

"There’s a rule around here," said Rep. Ron Kind, D-Wis., a leader of the pro-trade Democrats in the House. "If you’ve got the votes you call the vote, and you don’t take chances by sending people home again."

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