Mr. Obama’s dream of overhauling the nation’s health care system...

WASHINGTON — Speaker Nancy Pelosi was at her wits’ end, and she let President Obama know it.

Scott Brown, the upstart Republican, had just won his Senate race in Massachusetts, a victory that seemed to doom Mr. Obama’s dream of overhauling the nation’s health care system. The White House chief of staff, Rahm Emanuel, once Ms. Pelosi’s right hand man on Capitol Hill, was pushing Mr. Obama to scale back his ambitions and pursue a pared-down bill.

Mr. Obama seemed open to the idea, though it was clearly not his first choice. Ms. Pelosi scoffed.

“Kiddie care,” she called the scaled-down plan, derisively, in private.

In a series of impassioned conversations, over the telephone and in the Oval Office, she conveyed her frustration to the president, according to four people familiar with the talks. If she and Harry Reid, the Senate Democratic leader, were going to stick out their necks for Mr. Obama’s top legislative priority, Ms. Pelosi wanted assurances that the president would too. At the White House, aides to Mr. Obama say, he also wanted assurances; he needed to hear that the leaders could pass his far-reaching plan.

“We’re in the majority,” Ms. Pelosi told the president. “We’ll never have a better majority in your presidency in numbers than we’ve got right now. We can make this work.”

Now, in what could become a legislative Lazarus tale — or at least the most riveting cliffhanger of the Obama presidency so far— the House is set to take up the health bill for what Democrats hope will be the last time.

For Mr. Obama, who vowed earlier this month to do “everything in my power” to see the bill to fruition, the measure’s passage would be an extraordinary triumph. Its defeat could weaken him for the rest of his days in office.

That Mr. Obama has come this far — within a whisper of passing historic social legislation — is remarkable in itself. But the story of how he did it is not his alone. It is the story of how a struggling president partnered with a pair of experienced legislators — Ms. Pelosi and, to a lesser extent, Mr. Reid — to reach for a goal that Mr. Obama has often said had eluded his predecessors going back to Theodore Roosevelt.

Their journey over the last two months, interviews with White House aides, lawmakers, outside advisers, lobbyists and political strategists show, involved tensions, resolve, political spadework — and a little bit of luck.

When Anthem, a California insurer, notified policyholders of an increase in premiums of up to 39 percent, the move played right into the hands of a White House that had spent months demonizing the insurance industry.

A cross-Capitol feud erupted when Ms. Pelosi demanded that Mr. Reid provide a letter with the signatures of 51 senators willing to pass a package of legislative changes under the complex parliamentary procedure known as reconciliation. (On Saturday, the leader announced that he had a “significant majority.”)

And Mr. Obama’s decision to hold a bipartisan health care summit meeting proved a strategic success. The move privately mystified some Democrats. But it created an important cooling off period and helped shift attention to Mr. Obama and away from Capitol Hill, freeing the speaker to work on convincing recalcitrant members of her caucus that it would be politically disastrous for them simply to walk away.

Mr. Obama did not need any prodding from Ms. Pelosi, his aides say. The Scott Brown election came on the eve of his first anniversary in office, and he told aides he was irritated that his presidency appeared to be stalled. He was eager to do what he had done so often in the presidential campaign: cast caution aside in favor of bold action.

“We are this close to the summit of the mountain,” Mr. Obama told his close advisers in a meeting in late January, said one participant. “We need to try one more time.”

Responding to a Setback

The polls were still open in Massachusetts on Jan. 19 when Mr. Obama met in the Oval Office with David Plouffe, his top outside confidant and former campaign manager. Mr. Brown’s victory — he would take Senator Edward M. Kennedy’s old seat — was all but certain, and Mr. Obama’s 60-vote supermajority in the Senate had suddenly vanished.

Mr. Brown had made clear his objections to the health care legislation. “One thing is clear,” he proclaimed on election night, “voters do not want the trillion-dollar health care bill that is being forced on the American people.”

At that moment, the president did not know whether, or how, to proceed. The House and Senate had passed different versions of the bill and could not come to terms. Republicans were unified in their resistance. He considered his options, including Mr. Emanuel’s “skinny bill.” Whatever the course, aides said, Mr. Obama was insistent that health care not be put into a “time capsule,” never to be opened again in his tenure.

Tom Daschle, a close outside adviser, said Mr. Obama believed that health care would be his legacy. “This is what his presidency is about,” he said.

On Jan. 21, Representative Barney Frank, a Massachusetts Democrat and a powerful committee chairman, headed to the White House for a banking industry announcement. He had been openly skeptical about the prospects for the health measure