From MilitaryTimes.com:

Johnson said he and other law enforcement and security officials around the world were focused on foreign fighters heading to the bloody war, including those from the United States, Canada and Europe.

U.S. intelligence officials have said a handful of Americans and hundreds of Europeans have already returned to their home countries. The officials spoke on condition of anonymity because they were not authorized to speak publicly on the topic.

Syria isn’t the problem, it’s the people who traveled there and are now in this country.