Even as American convoys rolled up to oil fields in the eastern province of Deir ez-Zor over the weekend, officials inside the Donald Trump administration worried that the president could again reverse course on his on-again, off-again decision to keep US troops in Syria.

Asked whether the Pentagon was worried that Trump might reverse his decision, a senior administration official answered, “Yes.” The official added, “There is a lot of concern [that] he will.”

Trump has three times called for US troops to leave Syria, first in April 2018 and then in December, culminating in an October call with Turkish President Recep Tayyip Erdogan that led to a Turkish incursion into Kurdish-held northern Syria. But each time, the Defense and State Departments have salvaged a residual presence despite Trump’s push for a full withdrawal.

But Trump’s back-and-forth track record on Syria has made administration officials worried that the commander in chief could order yet one more hasty withdrawal. Asked if 900 US troops that have reentered Syria after a majority of American forces left would be a sustainable number, the senior official said Trump “may not think so.” Al-Monitor’s Amberin Zaman first reported on the potential of a residual American troop presence in Syria in October.