Dimon loses his sparkle

Activists march down Wall Street holding a cutout of Jamie Dimon during a protest against bank practices in New York last week

The exact details of the loss-making trades transacted by the London unit of J.P. Morgan’s chief investment office CIO are unclear, but the consequences for the bank’s senior management should be devastating.

Yet, it is curious that Jamie Dimon, the bank’s chief executive, has so far largely managed to escape the opprobrium that other bosses have received in recent years after their banks’ commercial failures. As a highly prominent advocate for the banking industry’s campaign against what it...