Citigroup ( C) is a mess.From the moment Wells Fargo ( WFC) snatched Wachovia from under Citi CEO Vikram Pandit bank in October, Citi has stumbled. Its stock price since then has plummeted from the low $20s to the mid-$3s today, as the market fears its decision to sell its Smith Barney business to Morgan Stanley ( MS) will fail to quench its need for capital in the coming months. So what caused this massive implosion? A lot of Citi watchers have assigned blame for the large drop in the bank's market cap, from $300 billion to $30 billion. Pandit has been widely characterized as a weak and indecisive CEO in the press. The New York Times blamed Bob Rubin and risk management headed by Tom Maheras -- both are now gone. In a recent interview, large Citi shareholder Prince Alwaleed bin Talal pointed the finger at former CEO Chuck Prince. A few (including John Reed, the man who merged Citi with Travelers in 1998) have also pinned Citi's shortcomings on the "financial supermarket" model masterminded by Sandy Weill. (On Tuesday, Pandit announced Citi would dismantle that supermarket model, returning to its old Citicorp roots.) It turns out that Citi's biggest mistake leading to its downfall did occur in 1998, but it wasn't the April super-merger of Citicorp and Travelers -- it was the November ousting of Jamie Dimon by then-Chair and CEO Sandy Weill over a disagreement with Weill's daughter.