[...] his words — by design or coincidence — mirror the nub of a policy argument the administration is wrestling with in the final months of Barack Obama's presidency. Asked at this week's debate whether he supports the decades-old U.S. policy of refusing to rule out being the first to use nuclear weapons, Trump at first said, "I would certainly not do first strike." During a Republican primary debate he was asked his view on modernizing the three main elements of the U.S.