My response...

I don't know.

I am absolutely positive that there are historical examples of the FBI and numerous (probably ALL) local and State agencies using under-cover techniques to find intel about suspected terrorist groups within the US. The "neo-Nazis", the Klan, the Black Panthers, SDS, the Weathermen, etc. ALL had domestic intelligence services investigating them from the inside and the outside. More recently, the radical "militias" and fundamental Islamic groups here in the US have also had their share of "spies" I'm sure.

The powers of the Federal Law Enforcement agencies are broad and rather sweeping, to the best of my knowledge, especially since 9-11. States have their investigative powers defined by both the US Constitution and their own State Constitutions... and most are also quite broad.

Was it "constitutional" for the FBI to investigate and infiltrate organizations like MLK's inner circles, or to arrest and hold thousands of Americans ONLY because they were of Japanese or German decent? Probably not... but what much of America forgets is that since 1921, the US Federal court system has determined that "evidence" in a criminal investigation that is obtained illegally (i.e. "fruit of the poisoned tree") CANNOT be used against those being investigated... not EVER.

Now, some officials have said that simply "breaking the silence" is enough to stop a criminal action from happening. I take this to mean that it is often enough to bring the criminals to "light" through the investigative process, even if the evidence can't be used in a prosecution. I don't know enough about this to judge... so I leave it to my State Attorney General and local D.A.s. If the problem is solved even without a court case, I'm fine with that. That's how they got Capone, after all.

It doesn't matter to me that the most radical mosques in America are investigated to ensure that they are NOT cooperating with terrorists... as long as Christian churches that promote violence against American medical facilities that perform abortions are also investigated just as vigorously, or that Christian churches that promote violence against US Armed Forces veterans because of their service (like that one in Kansas) is also investigated to the fullest extent of the Law. It is the role of the Federal Government to ensure domestic security and tranquility... and having a mosque or a church that actively works to hurt this nation or its citizens falls under this jurisdiction.