Why should we care about what’s in these guarantees? Here’s your answer:

Merrill Lynch & Co., which was bought by Bank of America, was the underwriter for $49.4 billion in defaulted collateralized debt obligations, the most of any bank, since October 2007, according to data compiled by Standard & Poor’s and Bloomberg.

Merrill was the biggest CDO underwriter from 2005 to 2007, with more than $102 billion, said Sanford C. Bernstein & Co. research analyst Brad Hintz.

Since October 2007, Bank of America underwrote under its name $15.1 billion in failed CDOs, according to S&P and Bloomberg. Banks have so far understated losses on such securities, and “the tsunami is on the horizon,” Hintz said.

Past sales of CDOs valued them at pennies on the dollar. In July, New York-based Merrill sold $30.6 billion of the securities to an affiliate of the Dallas-based investment firm Lone Star Funds for $6.7 billion. Merrill provided financing for about 75 percent of the purchase price, and the sale valued the CDOs at 22 cents on the dollar.

“By June, it’ll become clear that these guarantees are being drawn and they’re going to be huge,” said Christopher Whalen, managing director of Institutional Risk Analytics, a financial-services research company in Torrance, California. “Every day that goes by, Congress figures it out just a little more.”

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Ryan Chittum is a former Wall Street Journal reporter, and deputy editor of The Audit, CJR's business section. If you see notable business journalism, give him a heads-up at rc2538@columbia.edu. Follow him on Twitter at @ryanchittum.