Pakistan's Supreme Court struck down a political amnesty law Wednesday and ordered corruption cases against the country's pro-Western President, Asif Ali Zardari, and thousands of other politicians reopened.

The decision throws Pakistan, a crucial ally in the U.S. war against Islamic extremists, into a political crisis that's likely to undermine Zardari, divert his government and strengthen the country's military leaders, who so far have disregarded the Obama administration's requests to move against al Qaida, Afghan militants based in Pakistan and Pakistani militant groups.