BofA acquired MBNA for $35 billion in 2005, creating one of the largest credit-card issuers in the world. But now that strained consumers are relying more heavily on plastic to finance their lives amid layoffs, pay cuts and declining household wealth, analysts and economists have speculated that credit cards may be the next shoe to drop in terms of toxic debt.

Last July, BofA snapped up Countrywide Financial, the country's largest mortgage lender and servicer, in an all-stock, as it teetered on the brink of collapse. The deal seemed like a bargain at the time, despite Countrywide's heavy exposure to subprime mortgages. But now the economy has worsened and defaults have spread to less and less risky housing debt, bringing up questions about BofA's exposure.

Then came the ill-fated Merrill deal.

Months after the Countrywide acquisition closed, the financial markets spun into deeper turmoil, with Lehman filing for bankruptcy in September, followed days later by emergency bailouts of Fannie, Freddie and AIG. Counterparties and investors sensed guilt by association, punishing other Wall Street firms, especially Merrill Lynch, whose heavy exposure to subprime mortgage securities threatened the firm's solvency.

Lewis smelled a bargain and bought Merrill in an all-stock deal, in an effort to beef up BofA's brokerage and investment banking operations. But losses escalated from Merrill's troubled assets and Bank of America considered walking away from the deal. It sought additional funds from the government instead, leading investors to question the due diligence Lewis performed before inking the Merrill deal, and creating more uncertainty about what troubles lay ahead for BofA.

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