Trump's homeland security adviser becomes latest White House official to resign

Donald Trump's Homeland Security adviser, Tom Bossert, has resigned, the U.S. president's spokesperson says the latest in a string of senior advisers to leave the White House.

An administration official said Bossert, a former deputynational security adviser to President George W. Bush, had left at the request of Trump's new national security adviser, JohnBolton, who began working at the White House onMonday.

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

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

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

'Huge mistake'

The partial purge raised concern from Democratic SenatorChris Coons, a member of the Senate foreign relations committee,who told CNN that Bolton "seems to be swiftly moving to eliminate orto move toward an early retirement several of the president'sadvisers."

Jamil Jaffer, a former chief counsel to the Senate foreign relations committee and associate counsel to Bush, said it was a"huge mistake" to force Bossert out.

"Tom is a very smart and highly skilled national securityleader who has been a beacon of principle, capabilityand discipline in an otherwise chaotic White House," he said in astatement. "Letting Bossert go at a time of heightened threats, and when there is significant churn on the overall nationalsecurity team, is a yet another unforced error."

Bossert joins a long list of other senior officials who haveresigned or been fired since Trump took office in January 2017,including previous national security advisers Michael Flynn andH.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 Priceand Veterans Affairs Secretary David Shulkin have also left.

Bossert oversaw the administration's work on cybersecurity 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'sdecisions in recentmonths to blame and impose costs on each of those countries inan effort to create a more forceful cyber-deterrence strategy.

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

Rob Joyce, the White House's cybersecurity czar, whoreported to Bossert, is still working in the administration, a White House official said.