Obama and his aides know they are taking a big risk. “It’s a huge gamble,” says the senior administration official. The administration knows, for example, that al Qaeda, which has active cells in Libya, will try to exploit the power vacuum that will come with a weak or ousted Gaddafi. They also know that the U.S. will have to rely on other countries for the crucial task of rebuilding Libya and that the region may in fact be further destabilized by intervention. Outweighing that, the National Security Council’s Ben Rhodes says, are the long-term benefits of saving lives, protecting the possibility of democratic change elsewhere in the region and—tellingly—ensuring “the ability of collective action to be a tool in circumstances like this.”

One of the strongest voices in America for the idea of collective action to prevent war crimes is Samantha Power, a senior director at the National Security Council. In late 2006, Power told me that international humanitarian intervention had been “killed for a generation” by the U.S. invasion of Iraq. Then a professor at Harvard best known for her Pulitzer prize-winning history of America’s response to genocide (a book she wrote after covering the wars in Bosnia and Croatia and studying the genocide in Rwanda) Power was a strong believer in international intervention to prevent war crimes. Like many others, she was frustrated that the cause of preventing genocide had been undermined by George W. Bush’s unilateral intervention in Iraq, which discredited U.S. military action abroad and made building coalitions to stop war crimes seemingly impossible.