NewsScience & SocietyWhat nuclear weapons experts will watch for under TrumpResearchers will be monitoring arms control, the U.S. arsenal and the possibility of resumed tests The United States has undertaken a massive effort to modernize its nuclear arsenal, replacing or refurbishing its nuclear weapons and the missiles, submarines and bombers that carry them.U.S. Air Force photo/Airman 1st Class Devan HalsteadBy Emily Conover14 seconds agoIts a pivotal moment for nuclear weapons.Tensions between the United States and Russia, the two major nuclear powers,are high. Longstanding nuclear pacts have crumbled. China, which trails well behind the United States and Russia in nuclear arms, is beefing up its arsenal. North Korea is a nuclear threat, and Iran is on the threshold.Meanwhile, the United States is in the midst of an extensive update of its nuclear weapons. And when Donald Trump takes office as president on January 20, he will, for a second time, be responsible for those weapons. Here are some of the big issues well be watching.