Calling Monday's economic climate the most serious financial crisis since the Great Depression, Democratic presidential nominee Sen. Barack Obama attacked Sen. John McCain, R-Ariz., for supporting what Obama called a failing economic philosophy. On Sunday, the federal government declined to bail out Wall Street investment bank Lehman Brothers, another financial institution choked by the credit crisis. The ailing firm filed for bankruptcy this morning. Another Wall Street giant, Merrill Lynch & Co, narrowly avoided suffering the same fate by offering itself to Bank of America for sale.