America's oldest nuclear weapons, unwanted, outdated, a legacy of the 20th century, are now the focus of a political struggle that could shake the NATO alliance in the 21st. The questions hanging over the B-61 bombs, an estimated 200 of them on six air bases across Europe, relate not just to why they're still here, but to how safe and secure they are. For one thing, al-Qaida terrorists have already targeted this Belgian air base 84 kilometers (52 miles) northeast of Brussels. For another, U.S. Air Force inspectors found inadequate security at most of the six sites. And three months ago a "bombspotter" team, anti-nuclear activists, penetrated nearly one kilometer (a half-mile) inside Kleine Brogel, reaching its innermost bunkers.