WASHINGTON — Republican lawmakers this week pressed U.S. defense officials to explain why the military would need a new earth-penetrating nuclear weapon, which has been under evaluation in a program favored by the Bush administration (see GSN, Feb. 4). The administration has requested $8.5 million in fiscal 2006 funding for the Robust Nuclear Earth Penetrator program to continue a study of whether an upgraded, existing nuclear weapon might be capable of plowing more deeply through rock prior to a nuclear explosion. The money would enable a first drop test by the Air Force next year of the hardened weapon, without...