WASHINGTON, April 10 (Reuters) - U.S. President Donald Trump's homeland security adviser, Tom Bossert, has resigned, the president's spokeswoman said on Tuesday, in the latest departure from the White House of a senior adviser.

An administration official said Bossert, a former deputy national security adviser to President George W. Bush, had left at the request of Trump's new national security adviser, John Bolton, who began working in his post at the White House on Monday.

"The president is grateful for Tom's commitment to the safety and security of our great country," White House spokeswoman Sarah Sanders said in a statement.

"Tom led the White House's efforts to protect the homeland from terrorist threats, strengthen our cyber defenses, and respond to an unprecedented series of natural disasters," Sanders said.

RELATED: A look at Tom Bossert



13 PHOTOS White House Homeland Security Advisor Tom Bossert See Gallery White House Homeland Security Advisor Tom Bossert White House Homeland Security Advisor Tom Bossert gives a Hurricane Irma update during the daily press briefing at the White House in Washington, U.S. September 8, 2017. REUTERS/Jonathan Ernst U.S. acting Secretary of Homeland Security Elaine Duke and White House Homeland Security Advisor Tom Bossert speak to reporters after meeting with President Trump about hurricane relief efforts, at the White House in Washington, U.S. September 28, 2017. REUTERS/Jonathan Ernst White House Homeland Security Advisor Tom Bossert gives an update on the federal response to Hurricane Irma during the daily news briefing at the White House in Washington, U.S. September 11, 2017. REUTERS/Jonathan Ernst U.S. President Donald Trump's Homeland Security Advisor Tom Bossert announces that Trump today signed an executive order to bolster the government's cyber security and protect the nation's critical infrastructure from cyber attacks, during a news briefing at the White House in Washington, D.C., U.S., May 11, 2017. REUTERS/Kevin Lamarque White House Homeland Security Advisor Tom Bossert speaks at a Cyber Security Conference held at Tel Aviv University, Israel June 26, 2017. REUTERS/Amir Cohen U.S. President Donald Trump speaks to reporters after a security briefing at his golf estate in Bedminster, New Jersey U.S. August 10, 2017. Also pictured are National Security Advisor to the Vice President Andrea Thompson (L-R), White House Homeland Security Advisor Tom Bossert, U.S. National Security Adviser H.R. McMaster, Vice President Mike Pence and Central Intelligence Agency (CIA) Director Mike Pompeo. (REUTERS/Jonathan Ernst) White House Homeland Security Advisor Tom Bossert and White House Staff Secretary Rob Porter attend 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 Homeland Security Advisor Tom Bossert, was in attendance as President Donald Trump made remarks on combatting drug demand and the opioid crisis, in the East Room of the White House, on Thursday October 26th, 2017. (Photo by Cheriss May/NurPhoto via Getty Images) U.S. President Donald Trump, center right, speaks as Tom Bossert, assistant to Trump for the U.S. Department of Homeland Security, from right, U.S. Vice President Mike Pence, and Ricardo Rossello, governor of Puerto Rico, listen during a meeting in the Oval Office of the White House in Washington, D.C., U.S., on Thursday, Oct. 19, 2017. Trump said his administration's response to Hurricane Maria in Puerto Rico, where 22 percent of the islands residents have electricity and 72 percent have access to drinkable water, deserves a perfect '10' rating as he met with Rossello. (Kevin Dietsch/Pool via Bloomberg) U.S. Treasury Secretary Steven Mnuchin (C) and White House Homeland Security Advisor Tom Bossert (R) prepare to observe a moment of silence on the South Lawn of the White House October 2, 2017 in Washington, DC. The White House observed the moment of silence to honor of the victims of Sunday's mass murder in Las Vegas, the deadliest shooting in recent American history. (Photo by Chip Somodevilla/Getty Images) US President Donald Trump homeland security adviser Tom Bossert speaks during the White House Daily Briefing in Washington, DC, on August 31, 2017. (JIM WATSON/AFP/Getty Images) US Vice President Mike Pence (L) and Homeland Security Advisor Tom Bossert listen while Governor of Puerto Rico Ricardo Rossello and US President Donald Trump make statements for the press before a meeting in the Oval Office of the White House October 19, 2017 in Washington, DC. (BRENDAN SMIALOWSKI/AFP/Getty Images) Homeland Security Advisor Tom Bossert speaks during the daily briefing in the Brady Briefing Room of the White House on May 11, 2017 in Washington, DC. (MANDEL NGAN/AFP/Getty Images) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

Bolton's arrival at the White House also prompted the departure of Trump's national security council spokesman, Michael Anton.

Bossert joins a long list of other senior officials who have resigned or been fired since Trump took office in January 2017, including previous national security advisers Michael Flynn and H.R. McMaster, White House Chief of Staff Reince Priebus, communications directors Hope Hicks and Anthony Scaramucci, economic adviser Gary Cohn and chief strategist Steve Bannon.

Secretary of State Rex Tillerson, health Secretary Tom Price and Veterans Affairs Secretary David Shulkin have also left.

Bossert oversaw the administration’s work on cyber security issues and was considered a key voice for responding more aggressively to destructive cyber attacks launched by hostile adversaries, including Russia, Iran and North Korea.

He helped guide the administration’s decisions in recent months to blame and impose costs on each of those countries in an effort to create a more forceful cyber deterrence strategy.

Bossert was generally well respected by cyber security experts, who viewed him as a knowledgeable voice in the room.

Rob Joyce, the White House’s cyber security czar, who reported to Bossert, is still working in the administration, a White House official said. (Reporting by Jeff Mason, Steve Holland, Roberta Rampton, and Dustin Volz; editing by Jonathan Oatis)

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