An alleged terror plot in Boston is again raising questions about just how big the actual threat of homegrown terrorism is. Tarek Mehanna, 27, has been charged with plotting to “kill, kidnap, maim or injure” people in the United States. Prosecutors say Mehanna and others discussed attacking a shopping mall and two U.S. politicians. Explaining the case against Mehanna are Abby Goodnough, Boston Bureau Chief for The New York Times, and Richard Falkenrath, deputy commissioner of counterterrorism for the New York Police Department.