After vowing to end two wars, Obama may leave three behind

President Obama’s decision to expand the U.S. war effort in Iraq and Syria is a reflection of the conflicting pressures on a commander in chief who doubts that military force alone can end the conflicts in those countries, but who also feels compelled to act in the face of a humanitarian catastrophe and a growing threat to the United States.

The president on Friday said that he was sending about 50 Special Operations troops to northern Syria to work with Kurdish and Arab fighters battling the Islamic State. The deployment,...