JAMIE Dimon, America’s most famous banker, has had his 2012 bonus cut by half, to a measly $10 million. Good.

Dimon, the chief executive of JPMorgan Chase, will still have enough for tailored suits. But his pay cut publicly chastens him for allowing a bank trader to lose $6 billion in derivatives markets.

This trader, a Frenchman working out of the London office, was known in the markets as the London Whale. If the market sees the splash a man like that makes, so should his bosses. It is up to them to curb him, and they did not.

Chase bank earned more than $20 billion last year. Its stock is up, and it is not threatened by a $6-billion loss.

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But no bank can allow its traders to act as whales — at least not the largest bank in the United States, whose whales will make the largest splashes.

The public has an interest in this.

Four years ago, their money bailed out the big banks. The public has a right to insist that the trading desks of this federally insured bank employ no more whales, or else Dimon should lose the other half of his bonus, and his job.