The now-abandoned merger between pharmaceutical competitors Pfizer and Allergan (located in Ireland) has reignited debate over a longstanding hobby horse of tax reformers: Corporate inversions, where American companies take over foreign firms and incorporate abroad to reduce their tax burdens.

President Obama's charge — he called the practice "unpatriotic" — has taken a backseat to a new line of attack from Republican front-runner Donald Trump: Foreign countries are taking our jobs!