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The nation's Border Patrol chief is departing the role a day after President Trump signed an executive order greenlighting the construction of a massive wall on the U.S.-Mexican border.

Mark Morgan became the latest high-profile agency head to leave as the new administration takes over. The circumstances of his departure are unclear.

Customs and Border Protection U.S. Border Patrol Chief Mark Morgan, left, and Deputy Chief Carla Provost, testify during a hearing of the Senate Committee on Homeland Security and Governmental Affairs concerning border protection, on Capitol Hill, Wednesday, Nov. 30, 2016 in Washington. Alex Brandon / AP

His exit was announced by Kevin McAleenan, acting commissioner of U.S. Customs and Border Protection.

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"On behalf of the men and women of U.S. Customs and Border Protection and the U.S. Border Patrol, I want to thank Mark Morgan for his unwavering dedication to our border security mission, and recognize his life-long career in service to the nation," he wrote in a letter to the ranks.

Morgan did not release any statement about his departure.

A former FBI agent, Morgan had held the top post at the agency for just seven months and was the first outsider to head the agency since it was founded in May 1924.

But almost from the start, Morgan found himself at odds with the National Boarder Patrol Council, the union which represents the agents and which endorsed Trump early on in the presidential campaign.

It didn't help that Morgan's first job at the agency was investigating allegations of abuse against migrants by Border Patrol agents.

Morgan was appointed to that post in 2014 after James Tomscheck was removed by the Obama Administration following the release of a scathing report of the Border Patrol's use of force.

When Morgan was appointed chief, the union stepped up their criticism and eagerly aligned itself with Trump, who launched his campaign by vowing to build a wall on the border to keep out Mexican "rapists" and "criminals."