That JPMorgan Chase could lose $2 billion in risky trades involving bonds, with the nation still  recovering from a recession caused by big banks, might remind readers of the parable about the frog and the scorpion.

That's the one where a fearful frog agrees to give a beguiling scorpion a ride across a river on his back, only to be stung halfway across. "Why?" the frog asks, noting that they both will now drown.

"I couldn't help myself," replied the scorpion. "It's my nature."

So it is with America's mega-banks, it appears. They can't help themselves when it comes to taking on risky investments that endanger not only their livelihood if they fail, but the economy of the entire country. Do the words Lehman Brothers mean nothing to the crew directing JPMorgan?

To be sure, they are acting contrite now. And some heads will roll, including the bank's chief investment officer, Ina Drew, whom the bank announced Monday has retired. But the apology of JPMorgan CEO Jamie Dimon for an investment strategy that he now calls "flawed, complex, poorly reviewed, poorly executed, and poorly monitored" rings hollow.

This country simply cannot afford to keep putting its trust in institutions whose very raison d 'etre is to push their investment envelope to an extreme in search of maximum returns. The Dodd-Frank law that passed after the recession, which began in 2008, has yet to be fully implemented because the big banks insist they can be trusted. But once again, they have failed the test.

Congress shouldn't wait for another crisis to occur. It should act on pending legislation that would limit the nation's economic risk by limiting the size of banks. The 10 largest banks now hold assets greater than 60 percent of the national economy. That's too dangerous. Allowing the banks to keep their girth is like asking to be stung by the scorpion.