A merger between two pharmaceutical heavyweights -- New York-based Pfizer and Dublin-based Allergan -- is making history as the largest inversion transaction, but is drawing scrutiny from Capitol Hill and the campaign trail for the same reason. Democratic presidential candidates complained the merger could raise U.S. drug prices while sending tax dollars overseas, and key lawmakers seized the opportunity to push for overhaul of the U.S. tax code. But Pfizer defended the deal as a pro-consumer move aimed at creating...