Opponents say the Bush administration is writing the system of checks and balances out of the Constitution by placing the president's military powers above the civil authority of all three branches of the US government.
"Executive power to detain an individual is the hallmark of the totalitarian state," says Hamdi's lawyer, Frank Dunham, in his brief to the court.
One lesson from history likely to play a prominent role in the Hamdi and Padilla cases is that presidents act at the zenith of their power when their actions are authorized by Congress.
Truman lost the steel seizure case because he acted unilaterally without congressional approval. Roosevelt had the power to detain Japanese-Americans, but the military lacked any authority to enforce his executive order until Congress provided it. And Lincoln went to Congress and persuaded it to suspend the writ of habeas corpus, allowing him to indefinitely detain civilians.
"The Constitution requires that Congress, and not merely the president alone, determine how to deal with American citizens accused of conspiring with an enemy to commit war-like acts on American soil," says lawyer Carter Phillips in a friend-of-the-court brief in Padilla's case.
Government lawyers say the president obtained congressional authorization to detain citizens as enemy combatants when Congress passed a resolution in September 2001 authorizing the president to use "all necessary and appropriate force" against Al Qaeda. They note that the resolution also says "the president has authority under the Constitution to take action to deter and prevent acts of international terrorism against the United States."
Mr. Dunham and Donna Newman, Padilla's lawyer, say the authorization was intended to approve military action in Afghanistan, not the indefinite detention of citizens in US military prisons. They say Congress has passed other laws that bar the detention of Americans without constitutional protections.