When Obama vowed a redirection of U.S. policy in May 2011, the Arab Spring was young and hopeful. Tunisia and Egypt seemed on track toward democracy. In Libya, U.S. military force had helped depose a dictator; in Syria, peaceful demonstrations against another dictator were just beginning.

“In Damascus,” Obama said, “we heard the young man who said, ‘After the first yelling, the first shout, you feel dignity.’ ”

But Bashar al-Assad responded brutally, and his opponents took up arms. Obama predicted and wished for Assad’s imminent defeat, but he resisted calls from inside and outside his administration to help bring that defeat about, not with U.S. troops but by training and supporting the rebels.

By the time of Obama’s U.N. address, generals in Egypt had toppled the elected government, and Libya was plagued by uncontrolled militias. Worst, Syria was a humanitarian and foreign-policy disaster, with well over 100,000 people killed and millions more forced from their homes. In northern Syria, al-Qaeda affiliates were establishing the kind of safe havens that the United States went to war in Afghanistan to eradicate.

This can’t be an easy thing for a president to live with, as President Clinton made clear after Rwanda. So Obama fashioned a new doctrine.