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The US ambassador to Panama has resigned over differences with the Trump administration.

A State Department spokesperson told CNN that Ambassador John Feeley “has informed the White House, the Department of State and the Government of Panama of his decision to retire for personal reasons, as of March 9 of this year.”

According to an excerpt of his resignation letter that was read to CNN, Feeley’s decision was clearly prompted by differences with the Trump administration but was made well before Thursday’s reporting about President Donald Trump’s “shithole” comments.

“As a junior foreign service officer, I signed an oath to serve faithfully the President and his administration in an apolitical fashion, even when I might not agree with certain policies. My instructors made clear that if I believed I could not do that, I would be honor bound to resign. That time has come,” Feeley wrote.

The letter goes on to say that he leaves the embassy “in good hands” and the US relationship with Panama is “strong.”

Under Secretary of State for Public Diplomacy and Public Affairs Steven Goldstein told CNN that Feeley had submitted his resignation letter to the White House in late December.

“Everyone has a line that they don’t want to cross and we respect that,” Goldstein said. “We are sorry to see him go.”

Feeley was a career diplomat who was sworn in as ambassador in January 2016.

The spokesperson said Deputy Chief of Mission Roxanne Cabral will step in until a new ambassador is confirmed.

Panama will join the dozens of countries that do not currently have Senate-confirmed US ambassadors in place, including key US allies like South Korea, Jordan and Saudi Arabia.

While senior acting officials hold the reins in these important jobs, they are not permanent appointees and are limited in how long they can hold the roles.

Federal law allows these temporary officeholders to stay in the open jobs for, at most, 300 days. But 320 days have elapsed since the start of the Trump administration and acting officials in the State Department are starting to hit that limit, making presidential nominations more important than ever.