There is no oversight

Good expose by Glenn Greenwald on the fact that Congress does not and cannot oversee what the NSA does:

http://www.theguardian.com/commentisfree/2013/aug/04/congress-nsa-denied-access

It appears that such agencies are TOTALLY out of control. If Congress wants to restrain them, Congress will have to physically take over their facilities. Although the Sergeant at Arms of the Senate is authorized to arrest and detain any person violating Senate rules, including the President of the United States, the Sergeant at Arms of the House seems limited in power to the ceremonial use of the Mace of the House of Representatives. Since neither chamber has actual military or police powers, subduing the Executive Branch would be a difficult thing for them to accomplish.

IMPEACHMENT is the only real tool Congress has, and their refusal to use it amounts to acquiescence to the President's nefarious policies.