WASHINGTON, Dec 14 (Reuters) - U.S. President Donald Trump on Friday moved to end speculation that he was having a hard time finding a new chief of staff, naming his budget chief Mick Mulvaney to the top post on a temporary basis.

Mulvaney, a hard-charging conservative and former congressman, will be the third person in two years to try to bring order to what has often been a chaotic White House. Trump named him after two other prominent candidates withdrew from consideration in the space of a week.

"For the record, there were MANY people who wanted to be the White House Chief of Staff," Trump said on Twitter. "Mick M will do a GREAT job!"

The job is seen as one of the most important jobs in Washington: the gatekeeper to the president charged with marshaling the resources of the office to carry out his priorities.

I am pleased to announce that Mick Mulvaney, Director of the Office of Management & Budget, will be named Acting White House Chief of Staff, replacing General John Kelly, who has served our Country with distinction. Mick has done an outstanding job while in the Administration.... — Donald J. Trump (@realDonaldTrump) December 14, 2018

The most recent occupant - John Kelly, a retired Marine Corps general - had some success in restoring order after he was appointed in July 2017, but had a rocky relationship with Trump. Kelly will stay through the end of December.

Mulvaney will take the reins at a time when Republican Trump, weakened by Democrats winning control of the U.S. House of Representatives in elections last month, grapples with investigations into his businesses and most controversial policies. In addition, Special Counsel Robert Mueller is investigating whether there was collusion between Trump's 2016 election campaign team and Russian officials.

Mulvaney, 51, rose to prominence as a founder of the powerful House Freedom Caucus conservative voting bloc. He brings an in-depth knowledge of Congress to the job.

As head of the Office of Management and Budget (OMB), he has experience working with Trump and his top aides at the White House.

But the temporary nature of Mulvaney's appointment may undermine his authority in speaking for the president, and limit his ability to do the job, said Chris Whipple, author of a book on White House chiefs of staff called "The Gatekeepers."

"Donald Trump desperately needs a White House chief who can execute his agenda, and you can't do that if you have an expiration date on your forehead," Whipple said.

19 PHOTOS Acting White House chief of staff Mick Mulvaney See Gallery Acting White House chief of staff Mick Mulvaney White House chief of staff Mick Mulvaney announces that the G7 will be held at Trump National Doral, Thursday, Oct. 17, 2019, in Washington. (AP Photo/Evan Vucci) WASHINGTON, DC - OCTOBER 17: Acting White House Chief of Staff Mick Mulvaney answers questions during a briefing at the White House October 17, 2019 in Washington, DC. Mulvaney answered a range of questions relating to the issues surrounding the impeachment inquiry of U.S. President Donald Trump, and other issues during the briefing. (Photo by Win McNamee/Getty Images) Acting White House Chief of Staff Mick Mulvaney arrives to answer questions from reporters during a news briefing at the White House in Washington, U.S., October 17, 2019. REUTERS/Leah Millis WASHINGTON, DC - SEPTEMBER 08: White House Budget Director Mick Mulvaney speaks to members of the media after a House Republican Conference meeting September 8, 2017 at the Capitol in Washington, DC. Mulvaney was on the Hill to push for the Trump Administration's Hurricane Harvey relief and debt limit package. (Photo by Alex Wong/Getty Images) Mick Mulvaney, director of the Office of Management and Budget (OMB), holds up what he described as U.S. President Barack Obama regulations during a White House press briefing in Washington, D.C., U.S., on Thursday, July 20, 2017. Mulvaney has called Trump's tax-cutting approach to the economy MAGAnomics, a spin on Trump's campaign slogan, 'Make America Great Again' and has repeatedly attacked the Congressional Budget Office (CBO) for its estimates on the impact of Republicans' plans to repeal and replace Obamacare. Photographer: Andrew Harrer/Bloomberg via Getty Images Mick Mulvaney, Director of the Office of Management and Budget, speaks about 'MAGAnomics' during the daily press briefing in the Brady Press Briefing Room at the White House in Washington, DC, July 20, 2017. / AFP PHOTO / SAUL LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images) WASHINGTON, DC - JUNE 21: OMB Director Mick Mulvaney testifies during a Financial Services and General Government Subcommittee hearing on the budget for the Office of Management and Budget on Capitol Hill on June 21, 2017 in Washington, DC. (Photo by Astrid Riecken/Getty Images) WASHINGTON, DC - Budget Director for President Donald Trump, Mick Mulvaney explains and defends the administration's 2018 budget to the House Budget Committee on Capitol Hill in Washington, DC Wednesday May 24, 2017. (Photo by Melina Mara/The Washington Post via Getty Images) UNITED STATES - MAY 24: OMB Director Mick Mulvaney testifies before a House Budget Committee hearing in Longworth Building titled 'The President's FY2018 Budget' on May 24, 2017. (Photo By Tom Williams/CQ Roll Call) Mick Mulvaney, director of the U.S. Office of Management and Budget (OMB), listens during a House Budget Committee hearing on U.S. President Donald Trump's fiscal 2018 budget proposal in Washington, D.C., U.S., on Wednesday, May 24, 2017. Trump would dramatically reduce the U.S. government's role in society with $3.6 trillion in spending cuts over the next 10 years in a budget plan that shrinks the safety net for the poor, recent college graduates and farmers. Photographer: Andrew Harrer/Bloomberg via Getty Images WASHINGTON, DC - MAY 23: Office of Management and Budget Director Mick Mulvaney holds a news conference to discuss the Trump Administration's proposed FY2017 federal budget in the Brady Press Briefing Room at the White House May 23, 2017 in Washington, DC. Calling it a 'New Foundation for American Greatness,' the $4.1 trillion budget for would cut programs for the poor, including health care, food stamps, student loans and disability payments while offering big tax cuts for the wealthy. (Photo by Chip Somodevilla/Getty Images) Mick Mulvaney, director of the U.S. Office of Management and Budget, center, holds a volume of the fiscal year 2018 budget while speaking with Davita Vance-Cooks, director of the Government Publishing Office (GPO), left, during a tour of the GPO production facility in Washington, D.C., U.S., on Friday, May 19, 2017. Presidentï¿½Donald Trumpï¿½will send to Congress on Tuesday a proposal for balancing the federal budget within 10 years through deep cuts to discretionary and safety net spending, according to a U.S. official. Photographer: T.J. Kirkpatrick/Bloomberg via Getty Images WASHINGTON, DC - MAY 02: White House Press Secretary Sean Spicer (R) walks into the briefing room with OMB Director Mick Mulvaney (L) and Secretary of Homeland Security John Kelly (C), to brief the media on President Trump's budget, at the White House (Photo by Mark Wilson/Getty Images) Mick Mulvaney, director of the Office of Management and Budget (OMB), right, speaks as Gray Davis, former governor of California, listens during the Leaders In Global Healthcare and Technology (LIGHT) conference at Stanford University in Stanford, California, U.S., on Thursday, May 11, 2017. The LIGHT conference gathers leaders from a broad cross-section of executives and top policy makers in the health-care field to discuss the latest developments, challenges and opportunities shaping the healthcare industry. Photographer: David Paul Morris/Bloomberg via Getty Images WASHINGTON, DC - MARCH 16: Office of Management and Budget Director Mick Mulvaney arrives for a briefing in the Brady Press Briefing Room at the White House March 16, 2017 in Washington, DC. Mulvaney took questions about President Donald Trump's federal budget blueprint which was released Thursday. (Photo by Chip Somodevilla/Getty Images) WASHINGTON, DC - MARCH 13: U.S. Health and Human Services Secretary Tom Price (L) and Office of Management and Budget Director Mick Mulvaney talk to reporters following the release of the Congressional Budget Office report on the proposed American Health Care Act outside the White House West Wing March 13, 2017 in Washington, DC. Price said 'We disagree strenuously' with the findings of the CBO report about the Republican's attempt to repeal and replace the Affordable Care Act, or Obamacare. (Photo by Chip Somodevilla/Getty Images) US Vice President Mike Pence (R) delivers remarks before swearing in Mick Mulvaney (L) as Director of the Office of Management and Budget in Washington, DC, on February 16, 2017. / AFP / NICHOLAS KAMM (Photo credit should read NICHOLAS KAMM/AFP/Getty Images) WASHINGTON, DC - FEBRUARY 16: U.S. Vice President Mike Pence (C) Mick Mulvaney (L), swears as new Office of Management and Budget Director, as his wife Pam Mulvaney holds a bible during a ceremony in the Eisenhower Executive Office Building on February 16, 2017 in Washington, DC. (Photo by Mark Wilson/Getty Images) UNITED STATES - NOVEMBER 4: Reps. Mick Mulvaney, R-S.C., left, and Randy Hultgren, R-Ill., attend a House Financial Services Committee hearing in Rayburn Building titled Semi-Annual Testimony on the Federal Reserves Supervision and Regulation of the Financial System,' November 4, 2015. Federal Reserve Chairwoman Janet Yellen testified. (Photo By Tom Williams/CQ Roll Call) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

'CONTINUED AMBIGUITY'

Mulvaney, who has often defended Trump's economic policies on the closely watched Sunday political talk shows, has long been cited as a contender for the chief of staff job.

He has led budget talks with the U.S. Congress for Trump, including during a government shutdown in January. In 2013, with the House Freedom Caucus, Mulvaney helped orchestrate a government shutdown as a protest against funding for then-President Barack Obama's healthcare law.

Mulvaney and Trump face another funding deadline on Friday. If they cannot resolve an impasse with Congress, there will a partial government shutdown.

Even though Mulvaney was designated as "acting" chief by Trump, a White House official told reporters there was "no time limit" on his appointment.

Past presidents have also pulled in OMB directors to the post of chief because of their experience in negotiating with Congress, said Nick Kachiroubas of DePaul University, who has interviewed 11 former chiefs of staff.

Former Democratic President Bill Clinton elevated his OMB Director Leon Panetta to the job, as did former President Barack Obama with Jack Lew.

Mulvaney, though acting, will not be seen as "an outsider," giving him "more juice" in working with White House officials than a temporary chief otherwise might, Kachiroubas said.

"The big question we all ask is, why is this temporary?" he told Reuters.

"It only speaks to continued ambiguity in the White House."

Mulvaney will remain OMB director, and his deputy Russ Vought will handle the office's day-to-day operations, White House spokeswoman Sarah Sanders said.

FIRST AYERS, THEN CHRISTIE

For months, as his relationship with Kelly deteriorated, Trump had negotiated with Nick Ayers to take on the role. In a surprise move, Ayers, a Republican strategist and chief of staff for Vice President Mike Pence, declined the position on Sunday.

Ayers had wanted to do the job on an interim basis, but Trump had sought a two-year commitment, which Ayers ultimately rejected, sources familiar with the situation told Reuters.

15 PHOTOS Vice President Mike Pence's Chief of Staff Nick Ayers See Gallery Vice President Mike Pence's Chief of Staff Nick Ayers Vice President Mike Pence's Chief of Staff Nick Ayers, center, arrives for an event to salute U.S. Immigration and Customs Enforcement (ICE) officers and U.S. Customs and Border Protection (CBP) agents in the East Room of the White House in Washington, Monday, Aug. 20, 2018. (AP Photo/Andrew Harnik) Vice President Mike Pence's Chief of Staff Nick Ayers, center, arrives for a news conference with President Donald Trump and Republican congressmen after participating in a Congressional Republican Leadership Retreat at Camp David, Md., Saturday, Jan. 6, 2018. A seasoned campaign veteran at age 36, Ayers is emerging as a leading contender to replace White House chief of staff John Kelly, whose departure has long been the subject of speculation.(AP Photo/Andrew Harnik) White House Chief of Staff John Kelly, Ivanka Trump, White House senior adviser Jared Kushner, and Vice President Mike Pence's chief of staff Nick Ayers, listen as President Donald Trump speaks during a cabinet meeting at the White House, Thursday, March 8, 2018, in Washington. (AP Photo/Evan Vucci) White House Director of Legislative Affairs Marc Short, left, Vice President Mike Pence's Chief of Staff Nick Ayers, second from right, Counselor to the President Kellyanne Conway, third from right, and National Economic Council chairman Gary Cohn, second from right, listen and President Donald Trump and Republican congressmen speak at a news conference after participating in a Congressional Republican Leadership Retreat at Camp David, Md., Saturday, Jan. 6, 2018. (AP Photo/Andrew Harnik) FILE - In this Aug. 1, 2017 file photo, Vice President Mike Pence, left, attends a meeting with Georgia opposition leaders in Tbilisi, Georgia. Chief of Staff to the Vice President, Nick Ayers, is right. A seasoned campaign veteran at age 36, Ayers is emerging as a leading contender to replace White House chief of staff John Kelly, whose departure has long been the subject of speculation.(Zurab Kurtsikidze/Pool Photo via AP) Vice President Mike Pence's Chief of Staff Nick Ayers, center, arrives for a news conference with President Donald Trump and Republican congressmen after participating in a Congressional Republican Leadership Retreat at Camp David, Md., Saturday, Jan. 6, 2018. A seasoned campaign veteran at age 36, Ayers is emerging as a leading contender to replace White House chief of staff John Kelly, whose departure has long been the subject of speculation. (AP Photo/Andrew Harnik) U.S. Vice President Mike Pence, center, attends a meeting with Georgia opposition leaders in Tbilisi, Georgia, Tuesday, Aug. 1, 2017. Chief of Staff to the Vice President Nick Ayers is in the center right, and United States Ambassador to Georgia Ian Kelly, center left. (Zurab Kurtsikidze/Pool Photo via AP) WASHINGTON, DC - FEBRUARY 26: Chief of Staff to Vice President Pence Nick Ayers, left, and White House chief economic adviser Gary Cohn, listen as President Donald Trump speaks at a meeting with the members of the National Governors Association in the State Dining Room of the White House in Washington, DC on Monday, Feb. 26, 2018. (Photo by Jabin Botsford/The Washington Post via Getty Images) WASHINGTON, DC - OCTOBER 23: Vice President Mike Pence's Chief of Staff Nick Ayers (L) and National Security Advisor H.R. McMaster arrive in the Rose Garden before President Donald Trump and Singapore Prime Minister Lee Hsien Loong deliver joint statements at the White House October 23, 2017 in Washington, DC. Trump and Lee are meeting ahead of Trump's first official visit to Asia to attend the APEC and ASEAN meetings during the first two weeks of November. (Photo by Chip Somodevilla/Getty Images) WASHINGTON, DC - DECEMBER 5: Chief of Staff to the Vice President Nick Ayers stands outside a meeting with Senate Republicans on Capitol Hill, December 5, 2017 in Washington, DC. After the Senate passed their tax reform legislation last week, the next step will be a conference committee with members of the House to iron out the differences between the two bills. (Drew Angerer/Getty Images) WASHINGTON, DC - SEPTEMBER 07: Vice Presidential Chief of Staff Nick Ayers (L) talks with White House Counselor to the President Kellyanne Conway before a joint news conference with Amir Sabah Al-Ahmad Al-Jaber Al-Sabah of Kuwait and U.S. President Donald Trump in the East Room of the White House September 7, 2017 in Washington, DC. Following meetings and a working luncheon, the two leaders talked about their ongoing military cooperation and ongoing tensions in the Middle East. (Photo by Chip Somodevilla/Getty Images) Nick Ayers (L), chief of staff to U.S. Vice President Mike Pence, and White House Chief of Staff John Kelly look on as U.S. President Donald Trump holds a cabinet meeting at the White House in Washington, U.S. May 9, 2018. Picture taken May 9, 2018. REUTERS/Jonathan Ernst Nick Ayers (L), chief of staff to U.S. Vice President Mike Pence, and White House Chief of Staff John Kelly look on as U.S. President Donald Trump holds a cabinet meeting at the White House in Washington, U.S. May 9, 2018. Picture taken May 9, 2018. REUTERS/Jonathan Ernst Nick Ayers (C), Chief of Staff to ?U.S. Vice President Mike Pence?, attends as U.S. President Donald Trump presents the Medal of Honor to retired U.S. Army special forces medic Gary Michael Rose, for actions on a four-day secret mission to Laos in 1970 during the Vietnam War, in the East Room at the White House in Washington, U.S. October 23, 2017. REUTERS/Jonathan Ernst Nick Ayers (C), Chief of Staff to ?U.S. Vice President Mike Pence?, attends as U.S. President Donald Trump presents the Medal of Honor to retired U.S. Army special forces medic Gary Michael Rose, for actions on a four-day secret mission to Laos in 1970 during the Vietnam War, in the East Room at the White House in Washington, U.S. October 23, 2017. REUTERS/Jonathan Ernst Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

Trump insisted this week that he had a deep pool of "great people" lining up to push for the job. "I have so many people, I cannot interview them all," he told Reuters in an interview on Tuesday.

But hours before Trump announced Mulvaney's appointment on Twitter, former New Jersey Governor Chris Christie - seen as a frontrunner for the job - also withdrew his name from consideration.

Trump had been considering his son-in-law and senior adviser, Jared Kushner, and U.S. Trade Representative Robert Lighthizer as possibilities to replace Kelly on a long-term basis, sources familiar with the situation said.

This is not the first time Trump has turned to Mulvaney in a pinch.

Last November, he named Mulvaney the acting head of the Consumer Financial Protection Bureau, an agency that had been closely associated with former President Barack Obama's tenure.

The appointment was fought in court, but Mulvaney prevailed and ran the agency until earlier this month, when Trump's official pick was confirmed by the U.S. Senate.

(Reporting by Roberta Rampton and Steve Holland; Editing by Grant McCool and Sandra Maler)

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