In open hearings and behind closed doors, the Senate this week opened a broad - and often tense - dialogue with the Bush administration over the president's wartime powers.
It's more than just a probe into who authorized what, when, and why in a recently disclosed domestic eavesdropping program. If the president is not checked, lawmakers on both sides of the aisle argue, then the constitutional balance of power could shift away from the Congress for at least a generation.
"I'm for the president's inherent authority to conduct the war, but not to neuter the other two branches," says Sen. Lindsey Graham (R) of South Carolina, one of four Republicans on the Senate Judiciary panel to challenge the White House interpretation of presidential war powers.
During a day of questioning, Attorney General Alberto Gonzales defended the National Security Administration's warrantless surveillance of communication between US residents and suspected terrorists abroad as necessary, lawful, and limited by checks within the administration.
"Our enemy is listening," Mr. Gonzales told the Judiciary Committee on Monday, warning senators that further disclosure of the program, or ending it, would deprive the United States of a "key tool in the war on terror." He meets with the Select Committee on Intelligence in a closed hearing Thursday.
On its face, the NSA surveillance program is at odds with the 1978 Foreign Intelligence Surveillance Act (FISA), which Congress designated as the "exclusive" authority for wiretaps for intelligence purposes. The law has been updated five times to keep pace with changing needs.
During some seven hours of questioning, Gonzales refused to answer questions about how many Americans had phone calls or e-mails tapped by the NSA program, or whether it extended to opening first-class mail. These, he said, were operational questions that could jeopardize the effectiveness of the program.
But lawmakers did challenge the attorney general to explain why the Bush administration did not first come to the Congress to amend the FISA law, before opting to work around it.
They also questioned whether the government was using information gleaned from warrantless wiretaps to apply for warrants under the FISA process. If so, that could jeopardize current and future cases against suspected terrorists, they said.
Gonzales said the program is triggered "only when a career professional at the NSA has reasonable grounds to believe that one of the parties to a communication is a member or agent of Al Qaeda or an affiliated terrorist organization." As a check, the president reauthorizes approval for the program every 45 days - a time frame the administration set itself.
Moreover, Article II of the Constitution and the 2001 congressional resolution authorizing use of force give the president the authority to spy on enemies like Al Qaeda "without prior approval from the other branches of government," he said.
Such a legal interpretation of presidential powers is "a slippery slope," said Sen. Dianne Feinstein (D) of California, questioning Gonzales.
At the root of congressional worries about the NSA surveillance case is the prospect that such broad interpretations of presidential powers could last well into the future. "We could be in this war on terror for decades," says Sen. Sam Brownback (R) of Kansas.
Several senators cited the Federalist Papers as the authority for insisting on separation of powers and a strong system of checks and balances. "No man is allowed to be a judge in his own cause, because his interest would certainly bias his judgment...," wrote James Madison in Federalist No. 10.
In future hearings, the Justice panel is expected to call in outside legal experts and former Justice Department officials, including Attorney General John Ashcroft.
"The attorney general's repeated refrain was, 'Trust us' - we have all the necessary checks and balances within NSA and the Justice Department," says Bruce Fein, former associate deputy attorney general under President Reagan, a potential witness in the next round of hearings.
"The president's precedent is a permanent change in the constitutional landscape, because it has no endpoint to it. The privacy of our homes and conversations would depend solely on the discretion of the president," he adds.