CAMBRIDGE – In the summer of 2012, European Central Bank President Mario Draghi pledged to do “whatever it takes” to save the euro, including purchasing “unlimited” amounts of struggling governments’ bonds. The move, which has come to be known as the “Draghi put,” almost immediately reduced borrowing costs for Spain and Italy, and is widely touted as having pulled the eurozone back from the brink of disaster – without ever using the so-called “outright monetary transactions.”