President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE’s top homeland security aide, Tom Bossert, is resigning, the latest in a long line of staffers to exit the West Wing.

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

“President Trump thanks him for his patriotic service and wishes him well,” she added.

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Bossert has served in the White House since Trump’s inauguration and played a key role in responding to cyber threats and last year’s hurricanes that devastated Texas, Puerto Rico and the U.S. Virgin Islands.

Homeland Security Secretary Kirstjen Nielsen Kirstjen Michele NielsenDHS IG won't investigate after watchdog said Wolf, Cuccinelli appointments violated law Appeals court sides with Trump over drawdown of immigrant protections Democrats smell blood with new DHS whistleblower complaint MORE praised Bossert for providing “wise counsel” to Trump on a “range of current and emerging threats to our nation.”

His departure comes one day after John Bolton took over as national security adviser, a move that was expected to cause turnover on Trump’s security team. The 43-year-old aide is close to chief of staff John Kelly John Francis KellyMORE and Bolton’s predecessor, H.R. McMaster.

National Security Council spokesman Michael Anton announced his resignation two days before Bossert quit.

A veteran of the George W. Bush administration, Bossert was one of the few Trump aides to have previous White House experience.

Trump turned to Bossert in times of crisis, dispatching him to the White House briefing room and Sunday political talk shows to detail the administration’s relief efforts during last summer’s storms.

He also took the lectern at the White House to announce the U.S. had blamed North Korea for the massive “WannaCry” cyberattack that affected hundreds of thousands of computer across the world.

The timing of Bossert’s exit appeared abrupt.

He appeared on ABC News’s “This Week” on Sunday to speak about the administration’s response to the chemical weapons attack in Syria.

Bossert was also a keynote speaker Sunday night at The Cipher Brief's conference of national security experts in Sea Island, Ga. His remarks strongly suggested he did not expect to be forced out.

“The only thing that creates instability or the perception of it is (a) the [media] coverage, and (b) the turnover, and I think at this point we’ve reached what seems to be a decent stability point," Bossert said when asked what it is like to work in the White House. "I’m pretty comfortable with the president’s view of that, but it’s a little different.”

His departure continues the wave of staff turnover that has rocked the Trump administration.

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Top-level staff turnover at the White House has reached 49 percent, according to data compiled by Brookings Institution scholar Kathryn Dunn Tenpas, a number that has not been reached at this point in a presidency in decades.

Updated at 1:12 p.m.