I attended a taping of Justice Talking: Presidential Signing Statements on the 17th. The show will play on the radio station WHYY 91 FM at 3:45pm on December 4th (invitation). The show began with Host Margot Adler and guests Mickey Edwards and Christopher Schroeder, both of whom have worked in the government and have also taught as professors. They didn't disagree with each other as much as they took slightly different perspectives on presidential signing statements. As an historical overview, it was made clear to the audience that the current president did not invent signing statement and that they go back at least as far as Jimmy Carter (1976-1980). Signing statements are now used in very unique ways. They've never before contradicted the legislation just passed. Before G.W. Bush, they were always used to clarify what the legislation intended to do or to complain that the president would have used a line item veto if he were able.
The participants did not mention it, but Bush's particular use of signing statements goes back to current-Supreme Court Justice Samuel Alito's days as a member of the Reagan Justice Department.
The main question between the two speakers was over exactly what effect the signing statements were having. Schroeder was convinced they had no discernible effect while Edwards was convinced they were being used in some unknown, covert manner. The number of signing statements is not entirely clear as the Bush Administration has never given a definitive number, but it's around 750 to 800.
Speaking as a lefty liberal pro-Constitution kinda guy, I was quite pleased with the statements made by Senator Arlen Spector, who came on after the two debaters were done. Everything Spector said was completely in line with our liberal, pro-Constitutional point of view. One item I was especially pleased at hearing mentioned by him was the fact that the bureaucrats who carry out the detailed enforcement of the laws often use legislative histories to clear up various points in the legislation that do not speak for themselves. There's an excellent chance that they also see signing statements as similarly authoritative and use them while working out how to enforce the laws.
The Boston Globe was one of the first media sources to point out the current use of presidential signing statements.