The Supreme Court ruled Thursday that President Bush overstepped his authority in ordering military war crimes trials for Guantanamo Bay detainees.

The ruling, a rebuke to the administration and its aggressive anti-terror policies, was written by Justice John Paul Stevens, who said the proposed trials were illegal under U.S. law and international Geneva conventions.

Read more here.

UPDATE (6/30): See here for a very helpful analysis of the meaning of this decision in the context of the Uniform Code of Military Justice and the Geneva Conventions. The upshot is that because Congress approved the UCMJ and it uses the Geneva Conventions as one of the standards for the treatment of detainees the President cannot simply disregard those standards.

See also the discussion here (via Elfin Ethicist), which emphasizes the implications of this decision for the humane treatment of prisoners.