The European Central Bank appears increasingly willing to throw around its weight in bond markets to hold down borrowing costs for Spain — or at least wants traders to worry that it will. The euro and European stocks rose sharply Thursday after Mario Draghi, president of the E.C.B., said in London that the bank would “do whatever it takes to preserve the euro.” His comments were interpreted by some to mean that the E.C.B. might resume intervening in bond markets to keep borrowing costs for Spain and Italy under control. The E.C.B. would stay within its mandate, Mr. Draghi said in remarks at an investment conference. ... (full story)