Secretary of State Rex Tillerson. (Toby Melville/AFP/Getty Images)

AFTER MONTHS of incoherence, the Trump administration has taken a step toward a clear policy on Syria and its civil war. In a speech last week, Secretary of State Rex Tillerson bluntly recognized a truth that both President Trump and President Barack Obama attempted to dodge: that "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." To do that, the United States will continue to deploy several thousand personnel in the country and help allied Syrian forces maintain control over enclaves in the southwest, near Israel and Jordan, and the northeast, on the border with Iraq and Turkey.

Built into Mr. Tillerson's announcement was an implicit break with U.S. policy of the past several years, which was to seek Syria's pacification primarily through diplomatic deals with Russia. The regime of Vladi­mir Putin has repeatedly broken its word, backing the barbarous campaigns of the Syrian government to restore its control over the country by force. After agreeing a few months ago to support "de-escalation zones" in several parts of the country, Moscow is supporting new offensives against them. On Monday there were reports that Syrian forces had again used chemical weapons against rebel-held areas in the Damascus suburbs.

Critics predictably charge that Mr. Trump is launching another "endless war" in Syria. In fact, the administration has simply recognized reality: The United States cannot prevent a resurgence of al-Qaeda and the Islamic State, prevent Iran from building bases across Syria, or end a civil war that has sent millions of refugees toward Europe without maintaining control over forces and territory inside the country, just as Russia and Iran do. Only by being a factor on the ground will Washington be taken seriously as it seeks the implementation of a U.N. peace plan for Syria — a road map calling for nationwide democratic elections — that Russia and the regime of Bashar al-Assad are trying to bury.

Inevitably, the more robust U.S. position is prompting pushback from governments that were hoping to carve up Syria without regard for U.S. interests. One is Turkey, which objects to the fact that the U.S.-backed force in Syria's northeast is primarily Kurdish; strongman Recep Tayyip Erdogan has responded by launching an offensive against another Kurdish enclave on Turkey's border. That attack, too, has been quietly supported by Russia, which still hopes to goad Mr. Trump into following his original impulse to abandon Syria.

As Mr. Tillerson pointed out in his speech, to do that would be to repeat the mistake the United States made in Iraq, when "a premature departure . . . allowed al-Qaeda in Iraq to survive and eventually morph into ISIS." No one wishes to see U.S. forces bogged down in the Middle East for many more years, or a return to massive combat deployments. But the administration has rightly absorbed the lesson that the way out starts with a serious and sustainable U.S. commitment.