There's a reasonable chance — not a certainty — that Citi and [Bank of America], together, will lose hundreds of billions over the next few years. And their capital, the excess of their assets over their liabilities, isn't remotely large enough to cover those potential losses.
Arguably, the only reason they haven't already failed is that the government is acting as a backstop, implicitly guaranteeing their obligations. But they're zombie banks, unable to supply the credit the economy needs.
—Paul Krugman, "Banking on the Brink," The New York Times, February 23, 2009