WASHINGTON (Reuters) - The White House said on Monday that President Donald Trump would replace the head of the U.S. Secret Service, a day after Trump asked for the resignation of Homeland Security Secretary Kirstjen Nielsen.

Homeland Security Secretary Kirstjen Nielsen and U.S. President Donald Trump arrive to view a section of border wall in Calexico California, U.S., April 5, 2019. REUTERS/Kevin Lamarque

Nielsen and Trump had long clashed over immigration issues, and her departure came amid a surge in migrants from Central America at the southern U.S. border with Mexico.

Trump announced on Twitter that Kevin McAleenan, the current U.S. Customs and Border Protection commissioner, would become acting DHS secretary.

Randolph “Tex” Alles, the outgoing head of the Secret Service, said he had not been fired but that his departure was part of a broader shake-up of the Department of Homeland Security.

The White House said James Murray, a career Secret Service agent, would take over in May.

The Secret Service came under scrutiny after a Chinese woman carrying electronic devices was charged with bluffing her way through security checks at Trump’s Mar-a-Lago resort in Florida.

Trump’s White House has had the highest turnover of senior-level staff of the past five presidents, according to figures compiled by the Brookings Institution think tank.

Here are some senior figures who have been fired, quit or otherwise changed roles in the administration.

2019

Linda McMahon - The Republican fundraiser was one of Trump’s first Cabinet picks. She served as director of the Small Business Administration until March, when she resigned to join Trump’s re-election campaign. Trump nominated U.S. Treasurer Jovita Carranza to the position in April.

Clete Willems - A key figure in trade talks with China and a deputy to Trump’s top economic adviser, Larry Kudlow, Willems said in March he wanted to spend more time with his family.

Heather Wilson - The U.S. Air Force secretary, considered a top candidate to become the next defense secretary, decided to return to academia.

Bill Shine - Eight months after being hired as the White House communications director, he resigned to work on Trump’s re-election campaign. A source close to Trump said the president had lost confidence in the former Fox News executive.

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2018

Jim Mattis - In a candid resignation letter that laid bare his growing divide with Trump over Syria and Afghanistan policies, the defense secretary abruptly quit, shocking allies and Congress. Trump named Mattis’ deputy, Patrick Shanahan, a former Boeing executive, to the role in an acting capacity soon afterward.

Ryan Zinke - Trump’s first interior secretary left at the end of 2018 amid investigations into his use of security details, chartered flights and a real estate deal.

John Kelly - A retired Marine Corps general, Kelly was hired as White House chief of staff to bring order to the chaotic Trump White House, but ultimately fell out with his boss. Trump named his budget director, Mick Mulvaney, to the job on an acting basis on Dec. 14.

Jeff Sessions - The former Republican U.S. senator from Alabama was finally forced out as attorney general on Nov. 7 after months of being attacked and ridiculed by the president for recusing himself from a special counsel probe into Russian interference in the 2016 presidential election. He was replaced briefly by Matthew Whitaker until William Barr was confirmed to the job.

Nikki Haley - The former South Carolina governor stepped down at the end of 2018 as U.S. ambassador to the United Nations. Trump first put forward State Department spokeswoman Heather Nauert as her successor, but she later withdrew. Trump has since nominated Republican donor and U.S. Ambassador to Canada Kelly Craft for the position.

Don McGahn - Trump said in August the White House counsel would leave amid strains between the two over the Russia probe.

Scott Pruitt - The Environmental Protection Agency chief quit on July 5 under fire over a series of ethics controversies.

David Shulkin - White House officials said on March 28 that the Veterans Affairs secretary would resign.

H.R. McMaster - The national security adviser was replaced on March 22 by John Bolton.

Rex Tillerson - The secretary of state was fired by Trump on March 13 after long-standing tension between them.

Gary Cohn - The National Economic Council director and former Goldman Sachs president said on March 5 he would resign. Trump picked Larry Kudlow to replace him.

Hope Hicks - The White House communications director, a long-serving and trusted Trump aide, resigned on Feb. 28.

Rob Porter - The White House staff secretary resigned in February after accusations of domestic abuse from former wives.

2017

Omarosa Manigault Newman - The former reality TV star was fired as assistant to the president in December.

Tom Price - The Health and Human Services secretary quit under pressure from Trump on Sept. 29 over travel practices.

Stephen Bannon - Trump’s chief strategist was fired by Trump in mid-August after clashing with White House moderates.

Anthony Scaramucci - The White House communications director was fired by Trump in July after 10 days on the job.

Reince Priebus - Replaced as chief of staff by Kelly, Priebus lost Trump’s confidence after setbacks in Congress.

Sean Spicer - Resigned as White House press secretary in July, ending a turbulent tenure.

Michael Dubke - Resigned as White House communications director in May.

James Comey - The FBI director, who led the Russia probe before the special counsel was appointed, was fired by Trump in May.

Michael Flynn - Resigned in February as Trump’s national security adviser. Flynn later pleaded guilty to lying to the FBI.

Sally Yates - Fired in January by Trump as acting attorney general.