THE GAP between the policies pursued by President Trump’s administration and what the president says when he is outside the range of a teleprompter continues to be disconcertingly wide. At a rally in Ohio on Thursday, Mr. Trump suddenly blurted that he might hold up the trade accord his envoys just struck with South Korea “until after a deal is made with North Korea” — an assertion that left a lot of people puzzling over how perpetuating tensions with a critical U.S. ally could improve the prospects for negotiations with a common adversary.

That, however, wasn’t the most striking of Mr. Trump’s departures from his own national security strategy. After bragging that “we’re knocking the hell out of ISIS,” he announced that “we’ll be coming out of Syria, like, very soon. Let the other people take care of it now.” A day later it emerged that the president had suspended $200 million in stabilization funds for Syria after reading a news report about them.

That must have come as surprise to Defense Secretary Jim Mattis, U.S. commanders in the region and senior State Department officials — all of whom have been pursuing and publicly defending precisely the opposite policy for the last few months.

“We’re not just going to walk away [from Syria] right now,” Mr. Mattis said last November. “We’re going to make sure we set the conditions for a diplomatic solution . . . . Not just, you know, fight the military part of it and then say good luck with the rest of it.” Pentagon spokesman Dana White reiterated that position on Thursday, hours before Mr. Trump spoke, saying U.S. forces will work with local allies “to secure and stabilize liberated territory, as our diplomats work to resolve the Syrian conflict.”

The State Department agreed. “It is crucial to our national defense to maintain a military and diplomatic presence in Syria, to help bring an end to that conflict, and assist the Syrian people . . . to achieve a new political future,” then-Secretary Rex Tillerson said during a speech in January. He said the Trump administration was determined not to repeat the mistake the Obama administration made in Iraq, when “a premature departure . . . allowed al-Qaeda in Iraq to survive and eventually morph into ISIS.”

Does Mr. Trump agree with that position? The multiple other players in Syria, including Russia, Iran, Turkey and Israel, not to mention the regime of Bashar al-Assad, might understandably conclude that he does not. After all, the president has repeated versions of Thursday’s statement on several occasions. And though American forces have not pulled out of the large and strategically important territory they and Kurdish forces control in eastern Syria, there has been no sign of a U.S. push to end the civil war.

For now, even by Mr. Trump’s standard, U.S. forces must remain, as the Islamic State still controls several pockets of territory. But the president’s words will surely encourage Russian and Iranian hopes of driving the United States out of the country, so they can entrench their military bases and political influence. That would pose a major threat to Israel and severely damage U.S. standing throughout the Middle East. Which is why the Trump administration, as opposed to Mr. Trump, has concluded that letting “other people take care” of Syria is a terrible idea.

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