The federal government's website for children 6-8 years presents this information:

"One of the most important implied powers is Congress's authority to investigate and oversee the executive branch and its agencies, such as the Department of Defense and the Department of Justice. Congress also holds hearings on matters of general public concern. Sometimes members of Congress conduct these hearings to identify problems that create a need for new laws. In other cases Congress holds hearings to raise public awareness about an issue.

There are, however, some congressional powers that are rarely used such as the ability to impeach an official and amending the Constitution".

http://bensguide.gpo.gov/6-8/government/national/congress.html

-snip-

Maybe Tony Snow forgot about Congress' oversight responsibility because for at least the last 6 years it has been so rarely used.