U.S. stocks extend selloff into second day By: MarketWatch May 05, 2010 at 09:55 AM EDT U.S. stocks tumbled early Wednesday, hit by heightened concerns over Europe as violence erupted in Greece and a possible downgrade loomed over Portugal's debt. Read More >> Related Stocks: Alcoa American International Group Caterpillar Dow Jones Industrial Average (EOD) General Electric Merck & Co Procter & Gamble Time Warner Wal-Mart Stores, Inc.