U.S. Defense Secretary Jim Mattis said the U.S. is working with allies, including Turkey, to secure and stabilize Raqqa once Islamic State militants have been ousted. (May 9)

In deciding to arm Kurdish fighters in Syria, the White House made a risky choice Tuesday that places military expediency over broader diplomatic concerns.

The Kurds in Syria have proved to be the most effective fighters in the country against the Islamic State and they will play a critical role in liberating Raqqa, the militant group’s de facto capital in Syria.

But the Kurds are viewed by Turkey, a NATO ally and key partner in the war against the Islamic State, as terrorists linked to a violent separatist group inside its borders.

Read more:

“This is a mistake,” said James Jeffrey, a former U.S. ambassador to Turkey. He pointed out that Turkey in response could restrict or deny the U.S. military access to Incirlik, a military base used by U.S. warplanes to fly missions against the Islamic State, also known as ISIS.

“It’s hard to imagine a successful campaign against ISIS without our bases in Turkey,” he said.

In announcing the decision Tuesday, the Pentagon worked to temper Turkey’s concerns. “We want to reassure the people and government of Turkey that the U.S. is committed to preventing additional security risks and protecting our NATO ally,” Pentagon spokeswoman Dana White said in a statement.

But momentum is critical in warfare, and the Pentagon apparently determined it was better to press ahead with an offensive in Raqqa rather than wait to build broader diplomatic support. White House spokesman Sean Spicer said the move is designed “to assure a clear victory over ISIS” in Raqqa.

U.S.-backed forces in Syria have made headway in recent weeks in isolating Raqqa, a heavily defended city, and is preparing for an assault to clear the militants. The offensive is backed by U.S. air and artillery support, along with advisers working with the forces.

The Pentagon has said it wants to place military pressure on ISIS in Raqqa at the same time Iraqi forces are attacking in Mosul, making ISIS defend two critical cities simultaneously.

The campaign against the Islamic State in Syria is being led by the Syrian Democratic Forces, a loosely organized unit of about 50,000 fighters — about half Kurds and half Arabs — headed mainly by Kurds.

U.S. Central Command, which oversees military operations in the Middle East, has pressed the Trump administration to provide arms and other supplies to the Kurds. “They see no alternative ground force for seizing Raqqa,” said Chris Kozak, an analyst at the Institute for the Study of War.

The Pentagon policy had been to only provide arms and equipment to the Arab component of the Syrian Democratic Forces. But the fight for Raqqa will…