But it wasn’t enough to save Acosta from Mulvaney’s ire — and helps explain why the former federal prosecutor had such tepid administration support last week as he resigned over his handling of a high-profile sex-crimes case more than a decade ago.

The episode illustrates the growing influence wielded by Mulvaney, a former tea party lawmaker who has built what one senior administration official called “his own fiefdom” centered on pushing conservative policies — while mostly steering clear of the Trump-related pitfalls that tripped up his predecessors by employing a “Let Trump be Trump” ethos.

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This account of Mulvaney’s rising power is based on interviews with 32 White House aides, ­current and former administration officials, lawmakers and legislative staffers, some of whom spoke on the condition of anonymity to be candid. Mulvaney and the White House declined to make him available for an interview.

Mulvaney — who is technically on leave from his first administration job as budget director — spends considerably less time with Trump than his two previous chiefs of staff, Reince Priebus and John F. Kelly. And the president has sometimes kept him out of the loop when making contentious foreign policy decisions, advisers say. At a recent donor retreat in Chicago, Mulvaney told attendees that he does not seek to control the president’s tweeting, time or family, one attendee said. Priebus and Kelly had clashed with the president over his Twitter statements and the influence of his eldest daughter and her husband, who are senior advisers.

Instead, Mulvaney has focused much of his energy on creating a new White House power center revolving around the long-dormant Domestic Policy Council and encompassing broad swaths of the administration. One White House official described Mulvaney as “building an empire for the right wing.”

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He has helped install more than a dozen ideologically aligned advisers in the West Wing since his December hiring. Cabinet members are pressed weekly on what regulations they can strip from the books and have been told their performance will be judged on how many they remove. Policy and spending decisions are now made by the White House and dictated to Cabinet agencies, instead of vice versa. When Mulvaney cannot be in the Oval Office for a policy meeting, one of his allies is usually there.

“You have a chief of staff with a professional commitment to ensuring that a real policy agenda gets enacted,” said Charmaine Yoest, who served in senior roles in the Trump White House and at Health and Human Services before moving to the Heritage Foundation. “You’ve got to dig in, chart a path forward and stay committed to it, and we welcome his serious approach to policymaking.”

But Mulvaney also faces significant obstacles on Capitol Hill, where he made enemies on both sides of the aisle during his three terms as a bomb-throwing House conservative. Democrats openly disdain him as a saboteur, while many key Republicans distrust his willingness to compromise, particularly on fiscal policy. Some GOP senators freely signal they would rather deal with any other administration official than him.

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Mulvaney spends more time in his office than his predecessors, feeling no need to sit in on all of Trump’s meetings. He regularly huddles with Joe Grogan, a hard-liner who now leads the Domestic Policy Council, and Russell T. Vought, a conservative ally who runs the Office of Management and Budget in Mulvaney’s absence.

Advisers say a whiteboard in Mulvaney’s office has two items with stars beside them: immigration and health care. Immigration, however, is largely left to top White House adviser Stephen Miller and, to a lesser extent, presidential son-in-law Jared Kushner, with dim prospects for significant legislation on Capitol Hill. Passing any kind of health-care bill before the 2020 election is also unlikely, aides say, while budget cuts sought by Vought have died quickly in Congress.

Mulvaney’s biggest successes so far have come in deregulation efforts, where he prods agencies to move faster in case Trump loses or Democrats win the Senate in 2020, advisers say.

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Aside from the domestic policy shop, Mulvaney has also tapped allies to fill roles in the White House’s legislative affairs operation, the Office of Information and Regulatory Affairs, and his old haunts at the OMB. He regularly suggests ideas to all of them.

“What I am seeing is that Mulvaney cares about the domestic agencies much more than the prior chiefs of staff did,” said Tammy McCutchen, a former Labor Department official in the George W. Bush administration who is now a partner at the Littler Mendelson law firm. “They’re holding the agencies accountable to move forward on regulations.”

In the past two months, he has forced out the chiefs of staff at Health and Human Services, White House aides said, and the Labor Department amid policy disputes with them and their respective secretaries.

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Caitlin Oakley, an HHS spokeswoman, disputed the White House account. She said Peter Urbanowicz "left on his own accord and any statements to the contrary are 100 percent false." Late Sunday, Urbanowicz also said that he was not forced out, providing evidence from February and March of his intent to leave in June.

Mulvaney and Grogan have repeatedly clashed with HHS Secretary Alex Azar, overruling him, for example, on ending the funding of medical research by government scientists using fetal tissue.

Emma Doyle, Mulvaney’s deputy, has sought to control all presidential events and the president’s schedule — asking officials to submit formal proposals for why they should be in the room and controlling who is usually in the room. She also leads a weekly meeting on presidential events. Doyle was recently in charge of a review of the president’s immigration agencies and led a months-long hunt earlier this year for who was leaking the president’s internal schedules.

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“Everything is controlled. The only people not under his thumb are Kudlow and Bolton,” said one senior administration official, referring to economic adviser Larry Kudlow and national security adviser John Bolton.

Where Priebus and Kelly were more deferential to Cabinet members, Mulvaney has told them they are being judged on how much they can deregulate, with the policy council monitoring them daily. He is pushing for faster rollbacks of rules enacted by former president Barack Obama before Trump’s first term ends, such as restricting what falls under the Clean Water Act and halting implementation of higher fuel-economy standards, according to administration officials.

The president has blessed Mulvaney’s operation, White House aides said, and Trump considers his chief of staff an emissary to movement conservatives who have been vital to his presidency. But some Trump advisers say the president has no idea what Mulvaney and his aides do all day.

Mulvaney and Vought, among others, have sought to convince Trump to care more about cutting spending and the deficit. But Trump has rebuffed many of their proposed cuts as deficits soar.

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Trump recently told West Wing aides that Senate Majority Leader Mitch McConnell (R-Ky.) told him no politician had ever lost office for spending more money. Two people with direct knowledge confirmed that McConnell delivered that message in a June phone call about budget sequestration.

Although pleasing to businesses, Mulvaney’s efforts are also heartening to social conservatives, who say they are finding a more open reception than before.

For instance, a new rule released in May gives health-care providers, insurers and employers greater latitude to refuse coverage for medical services they say violate their religious or moral beliefs. That policy is facing legal challenges. The same month, the White House proposed a rollback of Obama-era rules that banned discrimination against transgender medical patients. Another rule, also being challenged in the courts, bans taxpayer-funded clinics from making abortion referrals.

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“We’re just taking the president’s challenge seriously to look everywhere and come up with options for deregulation that spurs economic growth,” Vought said in an interview. “You have an administration that’s in sync and everyone is talking to each other.”

Mulvaney — who has acknowledged to other advisers he knows little about foreign policy — has installed a deputy for national security, Rob Blair, who regularly battles with Bolton and his allies. Mulvaney and Bolton are barely on speaking terms, and Blair has regularly challenged Bolton’s subordinates, according to people familiar with the relationship.

Mulvaney has also been a key backer internally of Halil Suleyman Ozerden, whom Trump nominated for the U.S. Court of Appeals for the 5th Circuit last month despite misgivings from conservatives, according to people familiar with the matter. Ozerden and Mulvaney have known each other for years and Mulvaney was a groomsman in Ozerden’s wedding. Mulvaney vouched for him in a private conversation with Sen. Lindsey O. Graham (R-S.C.), who chairs the committee that will take up Ozerden’s nomination.

The former House Freedom Caucus member’s sway in Congress is clearly limited, however. GOP aides routinely trash Mulvaney in private and say he has done little to improve his image from his House days, when he was a leading antagonist in forcing government shutdowns and other hardball tactics. McConnell has told others on Capitol Hill that he would prefer to deal with Treasury Secretary Steven Mnuchin.

In a recent interview, Senate Appropriations Committee Chairman Richard C. Shelby (R-Ala.) paused for 10 seconds when asked whether Mulvaney was a productive force, particularly during a meeting with key principals in the office of House Speaker Nancy Pelosi (D-Calif.) in June.

Shelby finally responded that Mulvaney was “engaged” before pointing out that Mnuchin was the lead negotiator on behalf of the administration in the fiscal talks.

The bad blood between Mulvaney and Democrats is even more obvious.

Sen. Jon Tester (D-Mont.) recalled being pleasantly surprised when the White House contacted a half-dozen deal-minded Democratic senators in April, wanting to discuss the influx of migrant children at the border.

But he said there was no follow-up from the White House. Later, Tester saw Mulvaney on television complaining that the administration had met with Democrats on the border problems but that they weren’t working to address them.

“I think it was about Mulvaney being able to get on national TV and say, ‘We met with the Democrats,’ ” Tester said. “It was apparent to me that that was the political agenda behind it. It wasn’t about getting anything done. It was about laying blame.”

Mulvaney appears fully aware of his shortcomings with lawmakers, joking to others in the White House about his unpopularity on Capitol Hill. “I know they’d rather deal with Mnuchin,” Mulvaney has said, according to two White House officials.

Sen. Kevin Cramer (R-N.D.), who served in the House with Mulvaney, praised his performance but noted that senators are also able to talk to the president directly about any concerns.

“He’s not there to be a clerk. He’s there to lead,” Cramer said. “But I think it’s also clear that when the president says this is the position, that Mick’s more than capable of carrying out the president’s position. And I suspect in some cases they’re far apart — but in most cases, they’re pretty well in line.”

Mulvaney’s relationship with Trump has had its rocky moments. During a recent ABC News interview, the president berated Mulvaney on camera for coughing.

But the two men are unlikely to part ways, advisers say, partially because Mulvaney knows when to leave Trump alone — and is a good golfer.

“He takes the phrase chief of staff in the literal way. He’s the chief of the staff. He’s not chief of the president,” said Jonathan Slemrod, who led congressional outreach for Mulvaney at OMB until November. “He thinks Trump is a political genius and doesn’t second-guess a lot of his decisions.”

For his part, Mulvaney has joked about being an acting chief of staff, arguing there is no practical difference.

“You could make me the permanent chief of staff tomorrow, and he could fire me on Thursday,” Mulvaney said of Trump at a June 11 fiscal summit sponsored by the Peterson Foundation. “Or you could leave me as the acting chief of staff, and I could stay to the second term. It doesn’t make any difference.”

He added, “I’ll stay as long as I feel like he values my opinion and I like working for him, and both those things are happening right now.”