A more pressing concern than the border is that ISIS will establish a base of support within Jordan of men committed to violent subversion. The scenario is not far-fetched. From 2002-05 Jordan experienced a series of deadly terrorist operations perpetrated by ISIS’s antecedent, al Qaeda in Iraq, a group led by Jordan national Abu Musab al-Zarqawi. Jordanian militants today generally appear to be more sympathetic to the Syrian al Qaeda affiliate Jebhat al Nusra, but ISIS does have a cadre of supporters. On June 20 dozens of men demonstrated in support of ISIS in the town of Maan.

In April several Jordanian ISIS members fighting in Iraq posted a video on YouTube, invoking Zarqawi and shredding and burning their passports. The jihadists—one of whom is wearing an explosive belt—describe King Abdullah as “despotic” and “a worshiper of the English,” vowing to “slaughter” him.

Jordan takes the terrorist threat seriously—in 2013 it spent $1.3 billion, nearly 13% of its budget, on internal or homeland security and national defense. The U.S. provided the kingdom with more than $1 billion in 2013, including $360 million for economic assistance, $300 million in military aid, a $200 million supplemental cash transfer, and $140 million to care for nearly one million Syrian refugees.