The biggest sleeper cell in the US is the university professoriate - my niece goes to Arizona State U and her father told me this is what her professor said:
“She said in class the day after the Boston bombing that everyone should stop making a big deal out of it, that people die in other countries every day and we don’t care about it, and she mocked the statements and gestures of solidarity that people were making such as flying the Red Sox banner at Yankee stadium.”
Hope she immediately dropped that class.