Washington ? Sen. John McCain thought he had a deal when President Bush, faced with a veto-proof margin in Congress, agreed to sign a bill banning the torture of detainees.

Not quite.

While Bush signed the new law, he also quietly approved another document: a signing statement reserving his right to ignore the law. McCain was furious, and so were other lawmakers.

The Senate Judiciary Committee is opening hearings this week into what has become the White House’s favorite tool for overriding Congress in the name of wartime national security.

“It’s a challenge to the plain language of the Constitution,” the committee’s chairman, Sen. Arlen Specter, R-Pa, said in an interview with The Associated Press. “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.” Apparently, enough to challenge more than 750 statutes passed by Congress, far more than any other president, Specter’s committee says. The White House does not dispute that number, but points out that Bush is far from the nation’s first chief executive to issue them.

“Signing statements have long been issued by presidents, dating back to Andrew Jackson all the way through President Clinton,” White House spokeswoman Dana Perino said Monday.

Specter’s first hearing today is about more than the statements. He’s been keeping a laundry list of White House practices he bluntly says could amount to abuses of executive power – from warrantless domestic wiretapping program to sending up officials who refuse on national security grounds to answer questions at hearings.

But the hearing also is about countering any influence Bush’s signing statements may have on court decisions regarding the new laws. Courts can be expected to look to the legislature for intent, not the executive, said Sen. John Cornyn, R-Texas., a former state judge. “There’s less here than meets the eye,” Cornyn said. “The president is entitled to express his opinion. It’s the courts that determine what the law is.”

But Specter and his allies maintain that Bush, in practical terms, is doing an end-run around the veto process in the name of national security. In the sixth year of his presidency, Bush has yet to issue a single veto. Rather than give Congress the opportunity to override a veto with a two-thirds majority in each house, he has issued hundreds of signing statements invoking his right to interpret the law on everything from whistleblower protections to how Congress oversees the USA Patriot Act.