From Reuters ...

Citigroup Inc faced a crisis of confidence on Wednesday as investors questioned the survival prospects of the U.S. banking giant, and its shares tumbled 23 percent to a 13-year low.

The second-largest U.S. bank by assets has been reeling on concerns that mounting losses from credit cards, mortgages and toxic debt could overwhelm its efforts to slash costs and add deposits. Last month, Wells Fargo & Co dealt a blow by derailing Citigroup's bid to buy Wachovia Corp.

Citigroup shares closed down $1.96 at $6.40 on the New York Stock Exchange and have fallen 33 percent this week as some investors concluded that Chief Executive Vikram Pandit's plan to shed 52,000 jobs and cut expenses by one-fifth won't restore the bank to health.

"People are looking at their business model and wondering how on earth they're going to be able to survive," said William Larkin, a fixed-income manager at Cabot Money management in Salem, Massachusetts.