Slate has what seems a good article here, noting its follow-on to Hamdan vs Rumsfeld.
Let's hope a similar, thorough examination of signing statements is not far behind. Taylor quotes Justice Black:
The Constitution limits his functions in the lawmaking process to the recommending of laws he thinks wise and the vetoing of laws he thinks bad. And the Constitution is neither silent nor equivocal about who make laws which the President is to execute. The first section of the first article says that 'All legislative powers herein granted shall be vested in a Congress of the United States'Taylor ends by quoting Justice Warren:
Implicit in the term ‘national defense’ is the notion of defending those values and ideas which set this Nation apart. . . . It would indeed be ironic if, in the name of national defense, we would sanction the subversion of . . . those liberties . . . which makes the defense of the Nation worthwhile.