In his first term, he called for the ouster of Syria's Assad regime and said that its use of chemical weapons would be crossing a "red line." In his second term, he let the red line be crossed and allowed Putin to stage-manage Syria's agreement to relinquish the weapons.
In the process, the United States has abandoned attempts to depose Assad and now depends on his good faith to locate the weapons -- a victory for Putin and Assad's allies in Iran.
Obama's sharp reversals on Syria have been echoed by contradictory responses to China's declaration of an expanded Air Defense Identification Zone in the East China Sea, covering the Senkaku Islands owned by Japan but claimed by China.
Obama promptly ordered B-52s to fly through the ADIZ without notifying China. But the Federal Aviation Administration also told U.S. airlines to inform China when flying through this airspace. Japan and South Korea took a contrary stance.
Vice President Joe Biden, visiting China last week, expressed deep concern about the ADIZ and warned against armed clashes that could result. But he did not demand it be scrapped.
The November agreement with Iran, concluded after months of undisclosed U.S.-Iran negotiations, suspended sanctions for six months, but did not require the dismemberment of centrifuges demanded in previous United Nations resolutions.
America's traditional allies, Israel and Saudi Arabia, have made no secret of their opposition to this agreement. They fear a nuclear Iran dominating their region.
The American Interest's Walter Russell Mead sees the emergence of an unlikely Israeli-Saudi alliance against Iran, Russia and China, which he calls the "Central Powers" -- the term used for Germany's allies in World War I.
Today's Central Powers, he writes, are seeking to diminish U.S. power in the Middle East and East Asia, with some success. The U.S. is abandoning friends in the hope of reducing hostility from enemies.
Sudden reversals of policy, shifting alliances, secret negotiations -- these are reminiscent of Christopher Clark's statesmen who sleepwalked into World War I. Let's hope that clashes over Asian islets or Iranian centrifuges don't have the kind of consequences as that terrorist murder in Sarajevo did 99 years ago.