President Clinton announced today a total ban on U.S.nuclear weapons testing. His decision makes it more likely that negotiators in Geneva will succeed in passing a worldwide ban. Though Clinton's plan would allow for small-scale underground nuclear tests in the event of "supreme national interest," some members of Congress say more extensive testing is needed to ensure America's nuclear arsenal still functions properly. Ban supporters say computers can now do that job. Indeed, "the main reason the Pentagon has signed off on this is the incredible computing power now at their disposal," saysTIME's Mark Thompson. "And there's a growing sense at the Pentagon that the nuclear weapons aren't worth anything militarily any more -- an attitude that didn't exist ten years ago." The ban, which the president called an "historic milestone," comes fifty years after the U.S. dropped nuclear bombs on Hiroshima and Nagasaki.