George W. Bush and his most trusted advisers, Richard B. Cheney and Donald H. Rumsfeld, entered office determined to restore the authority of the presidency. Five years and many decisions later, they've pushed the expansion of presidential power so far that we now confront a constitutional crisis.

Relying on legal opinions from Attorney General Alberto R. Gonzales and Professor John Yoo, then working in the White House, Bush has insisted that there can be no limits...