Congress also has the authority to declare war, and by that very authority the authority to "undeclare" a war. Congress can, if it wishes, revoke the authority it gave the President right after the attacks of September 11, 2001, or any part of that authority.

Congress could, I suppose, "unmake" the Justice Department and every other Department not named in the Constitution -- including Homeland Security, the Department of Defense, the Department of the Air Force, etc.

In brief, Congress might not have "oversight" over the President (apart from impeachment) but it could make it impossible for him to do anything.