President Bush's assertion that his powers as commander in chief allowed him to authorize wiretaps on Americans despite a 1978 wiretapping law has little support in past Supreme Court rulings.
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The court laid out the limits of presidential power during wartime in a 1952 case stemming from former President Harry Truman's decision to seize a steel mill in order to avert a strike at the plant.
Fearing that a shortage of steel would hamper the Korean War effort, Truman decided to stop the strike. Although Congress had empowered him to keep the mill running by imposing a ''cooling off" period in labor negotiations, Truman chose to take more drastic action. Truman declared that the government would take control of the mill to ensure a steady supply of steel. But the court rejected Truman's claim that his powers as commander in chief allowed him to go beyond the will of Congress.
''When the President takes measures incompatible with the expressed or implied will of Congress, his power is at its lowest ebb," wrote Justice Robert Jackson in a much-cited concurring opinion.
http://www.boston.com/news/nation/washington/articles/2005/12/19/past_rulings_dont_support_bushs_use_of_war_powers/