President Donald Trump’s top aide for homeland security is leaving the administration, the White House said Tuesday.Tom Bossert’s resignation is reportedly at the behest of Trump’s new national security adviser, John Bolton, his third. In other words, Bossert is being fired. The White House has been besieged by staff shake-ups, resignations, and firings since Trump took office in January 2017.“The president is grateful for Tom’s commitment to the safety and security of our great country,” press secretary Sarah Huckabee 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. President Trump thanks him for his patriotic service and wishes him well.”Bossert held a position as a national security aide to President George W. Bush, and he assisted in drafting the federal government’s first official cybersecurity strategy in 2008.Bossert also worked in the Bush White House as the director of infrastructure protection policy.Cover image: U.S. Ambassador to United Nations John Bolton speaks at the National Oversight and Government Reform Committee on moving the U.S. Embassy in Israel to Jerusalem on Capitol Hill on November 8, 2017 in Washington, DC. (Photo by Tasos Katopodis/Getty Images)