Brooke Masters: On-site supervisors a good start for ECB

Banking union is the flavour of the month. Faced with investors who doubt the ability of some eurozone sovereigns to make good on their debts, the 17 members of the single currency have agreed to work together to channel aid directly to troubled lenders. But the deal is conditioned on the creation of a single banking supervisor, empowered to crack down on risky banks, no matter where they are located.

Setting up an impartial expert to oversee the banks could well be a key step toward restoring...