FRANKFURT (AP) — When European Central Bank head Mario Draghi said that he was ready to “do whatever it takes” to save the euro, he fueled investor hopes the bank would again start buying government bonds to lower borrowing costs for struggling countries.

Just one problem: the ECB has tried bond-buying before. And it didn’t work very well — the action was seen as too hesitant and fell short of decisively lowering borrowing costs for stricken Spain and Italy.