Has Snoopy just doomed us to another severe financial crisis? Unfortunately, that’s a real possibility, thanks to a bad judicial ruling that threatens a key part of financial reform.

Some background: When catastrophe struck the troubled U.S. financial system in September 2008, the proximate cause was the looming collapse of three companies — none of which were banks in the normal sense of the word, that is, institutions that take deposits and lend them out. One of them was, of course, Lehman Brothers; the other two were The Reserve, a money-market fund, and American International Group, or A.I.G, an insurance company.

Lehman declared bankruptcy, while The Reserve, which had lost money with Lehman, froze customers’ accounts, and was eventually forced into liquidation. A.I.G. was rescued by an $85 billion credit line from the Federal Reserve; in return, the Fed took 80 percent ownership of the company.

The episode showed that traditional financial regulation, which focuses on deposit-taking banks, is inadequate in the modern world. It’s not just that anyone who borrows short term to finance risky investments — which is what Lehman did — creates the same kind of danger as a conventional bank. There’s also a high degree of interconnectedness: A.I.G. wasn’t a bank, but it was selling guarantees on financial assets, and fears that it might fail to honor those guarantees threatened to topple dominoes across the economy.