The operative word being "generally". Political limitations are worthless. If they have the capability, they will abuse it. We already know they don't care about the constitution and that they have secret interpretations of laws.
Lets be frank here, Political limitations are the only thing stopping government agencies from shooting Laser Microphones half-a-mile away listening to your entire house. (4th Amendment, Illegal Search) You have no idea of the abuses that can be possible with law enforcement equipment, and are probably just scared of a little bit of the possibilities or powers afforded to them.
Keep your wits about you, this can get much much worse before it may get better. And hyperbole now will only harm your argument in the long run.
Reality is, intelligence agencies are under DoD. They aren't supposed to be investigating Americans, period. If they manage to nab information about American People (which includes legal immigrants btw), they are not allowed to forward it to law enforcement.
We know that anything pulled out of the NSA system is recorded and checked by the FISA courts, to ensure that Americans were not part of the targets. (Edward Snowden admitted it himself, although he wanted more than just 5% random checks on this log).
Why go through all the trouble when they can turn our cellphones into listening devices?
http://online.wsj.com/article_email/SB1000142412788732399700...
"We know that anything pulled out of the NSA system is recorded and checked by the FISA courts, to ensure that Americans were not part of the targets."
That is absolute bullshit! Have you not payed attention to the latest leaks on XKeyscore?
You left out the two intelligence agencies that are under the DoJ: the FBI and the DEA.