FBI Director Christopher Wray testified before the Senate in August that although there was no "imminent threat from a foreign terrorist organization on the border at the moment," terrorists are looking for any vulnerability to "exploit.” 

Andrew Arthur, a former immigration judge and legal fellow at the conservative Center for Immigration Studies, wrote in a June blog post: “We won’t know who the worst ones are until they act. But the worst ones are plainly coming.”

Source: The Washington Times