Trump and Putin spoke for one hour and vowed to join forces to fight terrorism in Syria and elsewhere, according to the White House and the Kremlin, signaling a potential shift in U.S.-Russian relations that have been marked by high tension.

Meanwhile, Trump signed a presidential memo directing the Pentagon to submit a plan within 30 days to defeat the Islamic State, an effort to make good on his campaign promise to more aggressively confront Islamist terrorism than his predecessor did.

Even prior to the memo, military officials had been at work developing potential actions for Trump and Defense Secretary James Mattis to consider. Those include potentially deploying additional advisers to Iraq and Syria, allowing U.S. military personnel to accompany local forces closer to the front lines, and delegating greater decision-making power to field commanders.