Al Qaeda training Americans in Syria?

http://www.cnn.com/video/data/2.0/video/world/2014/01/10/tsr-dnt-sciutto-al-qaeda-training-americans-in-syria.cnn.html

The Syrian civil war has been growing in intensity and scope for more than two years. Young liberal Americans have gone over to fight with the rebels against their government, most had been previously in the U.S. military. U.S. officials are questioning and worried that these Americans have been or may be the targets of Al Qaeda recruiters. The idea is that since they are American citizens and have all the right paperwork and documents to get back into the country that the young Americans would be ideal assets to carrying out terrorist activity within the United States. U.S. officials have taken the liberty of tracking these Americans documents, phones, emails, and social media to make sure that they are not a threat to the homeland. 

My question is, other than their presence in Syria what other cause have these Americans given to be tracked and suspected by the U.S. government? Do they really have the right to track their communications? Under the USA PATRIOT act of 2001 the government has the right to "intercept wire, oral, and electronic communications relating to terrorism." While I understand that there are precedented behaviors and situations that would cause this type of suspicion it doesn't seem quite right to me that the government is able to this with quite a small amount of probable cause against these Americans. But on the other hand I do understand it because how are U.S. officials supposed to stop tragedies like 9/11 without capitalizing on instances like these?