If the American public and political class won’t bear any U.S. military involvement in Iraq, why were troops dispatched to the country? And if ISIS overrunning the Kurds, taking control of key infrastructure, and carrying out a deliberate slaughter of the Yazidis isn’t enough to get the U.S. forces involved, is there anything that would force a U.S. military response?

The situation is dire, but legal constraints may limit U.S. options for direct assistance to the Kurds, said Douglas Ollivant, a former U.S. Army officer who advised Gen. David Petraeus and served in the National Security Council under Presidents George W. Bush and Barack Obama.

“There might not be a legal way for us to sell arms to the KRG [Kurdistan Regional Government],” Ollivant said. “The Kurds are finding out the hard way that there are huge structural barriers, totally independent of policy, being a sub-state unit.”