As Spain struggles to keep its banking crisis from turning into a Greece-style bailout (a battle it now appears to have lost), ratings agency Fitch has dropped Spain's credit rating three notches, from A to BBB – just a step above junk status. This instantly jacks up the price the troubled country must pay to borrow the money it needs to stay solvent. And it raises once again a major concern about the Big Three ratings agencies: Fitch, Moody's and Standard & Poor. They wield so much market power that a single ratings "opinion" can trigger investor panics, making an already bad situation much worse.

The European Union is trying to rein in that power: this latest move shows how big a task that's going to be, and just how important it is.

Read more:Why do we listen to the ratings agencies?