After six years of kowtowing to the White House, Congress is finally challenging President Bush’s campaign to trample all legal and constitutional restraints on his power. Congressional committees have issued subpoenas for documents and witnesses in two major cases and have asked for the first — and likely not the last — criminal investigation of an executive branch official who might have lied to Congress. Predictably, the White House is claiming executive privilege and refusing to cooperate with the legitimate Congressional investigations, one springing from Mr. Bush’s decision to spy on Americans without a warrant and the other from the...