"There's this notion that the president is committing acts of civil disobedience, and he's not," said Mr. Bush's press secretary Tony Snow, speaking at the White House. "It's important for the president at least to express reservations about the constitutionality of certain provisions."
Signing statements are not new, reports CBS News correspondent Bob Fuss, nor is the power of the president to refuse to enforce a law he considers unconstitutional — at least until a court rules on it.
But a number of Democrats, and notably the Republican chairman of the Senate Judiciary Committee, Arlen Specter, say President Bush, who has never vetoed a bill, has abused signing statements as part of a pattern of taking greater powers.
Such statements have accompanied some 750 statutes passed by Congress, including a ban on the torture of detainees and the renewal of the Patriot Act.
"There is a sense that the president has taken signing statements far beyond the customary purview," Specter, R-Pa., said.
"It's a challenge to the plain language of the Constitution," he added. "I'm interested to hear from the administration just what research they've done to lead them to the conclusion that they can cherry-pick."
Democrats pounced, saying the signing statements are the latest example of the administration's expansion of executive power.
"I believe that this new use of signing statements is a means to undermine and weaken the law," said Sen. Dianne Feinstein, D-Calif. "If the president is going to have the power to nullify all or part of a statute, it should only be through veto authority that the president has authorized and can reject — rather than through a unilateral action taken outside the structures of our democracy."
A Justice Department lawyer defended Mr. Bush's statements.
"Even if there is modest increase, let me just suggest that it be viewed in light of current events and Congress' response to those events," said Justice Department lawyer Michelle Boardman. "The significance of legislation affecting national security has increased markedly since Sept. 11."