Both parties face a contentious political debate over the decision declaring military tribunals illegal as they look to capitalize on a national security issue ahead of crucial congressional elections in November.

"How do you go back to Chicago, Illinois, or Las Vegas, Nevada, and say 'You know what? The president is just being too mean to these people," said Don Stewart, spokesman for Republican Sen. John Cornyn of Texas. "That's a very difficult argument to make."

In Thursday's ruling, the nation's highest court found the tribunals, which Bush created right after the September 11 attacks for prisoners at Guantanamo Bay in Cuba, violated the Geneva Conventions and US military rules.

The White House has been accused of using the war against terrorism to grab executive power at the expense of the US Congress. Vice President Dick Cheney has spoken publicly about restoring the powers of the presidency after what he saw as "an erosion"' in the aftermath of the Vietnam War and the Watergate scandal.

The Bush administration has turned that tide in many ways, ranging from the fight to keep secret the deliberations of its energy task force, to its assertion of authority after September 11, including secret domestic surveillance and financial tracking programmes.

"The Guantanamo ruling is a repudiation of their entire governing philosophy," said Simon Rosenberg, founder of the centrist New Democrat Network. "This philosophy has failed. It's not only failed, it hasn't passed the test of the Supreme Court."