WASHINGTON — The quarterback Brett Favre has long retired. Cher shut down her most recent tour. Representative Nancy Pelosi — repeatedly written off and derided since her party lost the House in 2010 — powers on.

Ms. Pelosi, 74, maintains unwavering control over Democratic members of the House on legislation — in contrast to the House speaker, John A. Boehner, who continues to struggle with his cacophonous caucus — and she may be a surprisingly vital tool for the White House at the end of President Obama’s tenure.

Her lasting authority was demonstrated this week when she helped pass a measure from the Senate to avoid yet another government shutdown. That vote “strengthened our hand,” Ms. Pelosi said, a sentiment that many Republicans, who are eager to show that they can effectively govern, agree with, teeth clenched.

On the same day that she helped the vote to fund the Department of Homeland Security sail through the House thanks to Democratic support, Ms. Pelosi, the minority leader, served as the embodiment of White House rage over a speech by the Israeli prime minister, Benjamin Netanyahu, to a joint meeting of Congress.

As Mr. Netanyahu spoke, Ms. Pelosi fulminated on the House floor. She reignited her critics, who said her response was impolite at best, and they took the sorts of personal shots at her that have long marked her tenure. (Senator Lindsey Graham of South Carolina apologized for making a crack about her age.)

“If they thought I was rude,” Ms. Pelosi said during an interview in her Capitol Hill office as snow fell outside, “you can’t imagine how restrained I was!” Breaking for a millisecond from her normal studied dismissal of her omnipresent critics, she added, “I have endured so many around here.”

Ms. Pelosi’s continued reign often surprises, but it is based largely on her ability to manage her members, one at a time. It is generally easier to maintain cohesion in the minority, where members live to block the will of the majority. Further, two Republican waves in the House swept out most moderate Democrats, rendering the caucus more ideologically unified against Republicans, and more aligned with her brand of liberalism.

“I don’t think it takes a lot of skill to vote against an agenda,” said Representative Charlie Dent, Republican of Pennsylvania.

Should a Republican win the White House in 2016 and the Senate remain under Republican control, Democrats will almost certainly find themselves nearly debilitated.

Yet for now, from her perch in the minority, Ms. Pelosi could be Mr. Obama’s best weapon of protection in Congress on issues like foreign policy, energy and health care.

“We’re here to work in a cooperative way,” said Ms. Pelosi, who added that she often asked Mr. Boehner how she could help him. “But we have our standards, and we have our president.” She added, “Our leverage is sustaining his veto.”

While her personal allegiance to the president’s policies is not inalterable — it is possible that she will not support his trade agenda — she could give members the room to provide the White House the votes it will need on a policy that now enjoys more support from Republicans than from Democrats.

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“The White House places a premium on our success in continuing to closely coordinate our efforts with her,” said Josh Earnest, a White House spokesman.

While some Democrats have griped in recent years that it is time for new blood in their party’s aging leadership slate, few takers are in sight. An obvious heir apparent, Representative Chris Van Hollen of Maryland, 56, has said he will run for the Senate, even though Ms. Pelosi said she was trying to talk him out of it.

“I think he’s such an extraordinary talent,” said Ms. Pelosi, who added that she thought Mr. Van Hollen could run for president from his House seat. She conceded, “I think the caucus wants a generational change.”

Should he so choose, Ms. Pelosi also could end up being a partner to Mr. Boehner in avoiding future calamities, as she did on Homeland Security funding.

First, she told her members to reject a measure favored by House Republicans to fund the department for three weeks. Then she told them to pass a one-week measure as a bridge to yet another bill that the Senate passed to finance the department through the rest of the fiscal year. The House then quietly passed the full-year bill that Ms. Pelosi wanted after a week of bluster.

“When she told us to vote against the three-week bill, we voted against it,” said Representative Brad Sherman, a fellow California Democrat. “A few hours later, we voted for a one-week bill. There was no substantive difference between them. This was strictly a matter of party discipline.”

Jeh C. Johnson, the secretary of the Department of Homeland Security, made several trips to Capitol Hill to meet with lawmakers, and took a breather in Ms. Pelosi’s office, where she gave him a pep talk, he said. “Without the unqualified, unified support” of Democrats, Mr. Johnson said, “we wouldn’t have obtained our full-year appropriation.”

Notably, when the president is not aligned with her, she falters, as she did last year when she tried to block a huge spending bill that included a banking provision she disliked.

Nonetheless, some Republicans said their party could learn from Ms. Pelosi, particularly from her time as speaker, when the tables were reversed.

“They had a majority elected to end the Iraq war,” said Representative Tom Cole, Republican of Oklahoma, referring to the 2006 election that ushered in Ms. Pelosi’s speakership.

“It was enormously frustrating to them that they couldn’t do it,” Mr. Cole said, because, he noted, Republicans “had a presidential veto that could be sustained in either house.”

Ms. Pelosi’s other big moment last week came in her angry protest against Mr. Netanyahu’s speech, which began with her privately fuming at Mr. Boehner for inviting him, and her remarks about what she said was condescension from the Israeli leader. Mr. Netanyahu’s warnings about nuclear weapons were not needed, she said, even though Republicans “applauded their alleged hearts out, well, take out alleged,” she fumed.

The speech, which enraged the Obama administration, almost made her cry, she said. “That was significant to me that she chose to say that, because in the four years I worked for her I only saw her choke up once,” said Ellen Qualls, who served as a senior adviser during Ms. Pelosi’s speakership. The only other time she saw her choke up, she said, was during the Tea Party movement against a health care overhaul, when threats of violence were made against lawmakers and the president.

Ms. Pelosi was emulated in her language by many fellow House Democrats, and derided by Republicans. “She really does not take criticism personally,” said her daughter, Christine Pelosi. “She always, always said when we were kids: ‘You have to understand that criticism and effectiveness go hand in hand. You have to wake up and let today be a new day.’ ”