It's happened: An increasingly unpopular president has been confronted by a congressional subpoena for information about political decisions made at the highest levels of the executive branch.
The president well understands the danger of making one branch of the government privy to the confidential discussions of the other. For to grant Congress the power to compel testimony from his top-ranking aides is to upset the delicate balance between supposedly co-equal branches of government. How equal can they be if the legislative branch is given access to the candid, confidential discussions of the executive?
How long will such discussions remain candid if the president's aides - and future aides - realize that what they say in confidence may not remain confidential? Do we the people really want to deprive our presidents of such counsel? That's another reason for recognizing executive privilege: to assure that some confidential discussions remain confidential. Without that assurance, any advice a president receives might soon lose its value, for presidential advisers might not dare say what they really think.
Rather than heed the congressional summons, the president explained that, if he did, the constitutional separation of powers "would be shattered, and the president, contrary to the fundamental theories of constitutional government, would become a mere arm of the legislative branch of the government (for) he would feel during his term of office that his every act might be subject to official inquiry and possible distortion for political purposes."
The president who made that point wasn't George W. Bush this week but Harry S Truman in November of 1953, when the House Committee on Un-American Activities subpoenaed him to testify about what he knew about communists in government and when he knew it.
Mr. Truman knew better than to let that bunch start rummaging through his or his administration's confidential papers and discussions. After all, he'd once been a member of the U.S. Senate himself. And, as such, quite an investigator. If he hadn't defended the independence of the executive branch, his presidency and every successive one would surely have been significantly, maybe fatally, weakened.
Harry Truman was in good company. The doctrine of executive privilege is almost as old as the Constitution itself, and flows naturally from its separation of powers and creation of independent branches of government to check one another, not dominate another.