SOMETIMES a heckler can be a politician’s best friend. Giving
his fullest account of counter-terrorism policy for some years
in an hour-long speech to the National Defense University on May
23rd, President Barack Obama was repeatedly and loudly
interrupted by a woman protester demanding the immediate closure
of the Guantánamo Bay prison camp and greater respect for the
rule of law.  The heckling helped Mr Obama, whose speech had
until then felt like an address to a straw man—some imaginary
citizen of tender conscience who needed to be assured that
America was right to target terrorists with lethal drone strikes
in Pakistan or Yemen, and needed reminding that it was not that
easy to close Guantánamo or put terror suspects on trial in
mainland American courts.  True, left-wing supporters of the
president are upset with his use of armed drones, and hate the
idea that American guards and doctors are force-feeding more
than 100 detainees on hunger strike in Guantánamo. But most
ordinary Americans tell pollsters th