By Fred Burton and Scott Stewart U.S. counterterrorism sources remain concerned that an attack against the U.S. homeland will occur within the next two to three weeks. This is not surprising, considering that the drums have been beating loudly in Washington this summer about a potential attack — first from Homeland Security Secretary Michael Chertoff and then in the form of a National Intelligence Estimate . More recently, several other reports have appeared concerning an impending attack, including an alert over the weekend in New York triggered by an alleged dirty bomb plot . One of the reasons for the heightened concern is that most everyone, including STRATFOR, is surprised that no major jihadist attack has occurred on U.S. soil since 9/11. Many plots have been disrupted, and it is only a matter of time before one of them succeeds.