info on congressional subpoenas for interested folks:
Here's an excerpt, then the link:
Federal courts give great deference to congressional subpoenas. If the investigative effort falls within the "legitimate legislative sphere," the congressional activity---including subpoenas---is protected by the absolute prohibition of the Speech or Debate Clause . . .
http://www.senate.gov/reference/resources/pdf/RL31836.pdf
Ok, what does all that mean. :)