WASHINGTON — The Obama administration’s decision to curb the ability of U.S. corporations to skirt taxes by merging with foreign companies kicked off an immediate election-season debate over when and how to tackle the nation’s complex corporate tax code. Following through on a populist appeal from President Barack Obama for a new era of “corporate patriotism,” the Treasury Department stepped in Monday with new regulations designed to limit the ability of U.S. firms to seek refuge in lower …