US stocks tumbled on Monday dragging the benchmark indices to their biggest slump since December 2008, amid concern that a downgrade of the nation's credit rating by Standard & Poor's may worsen the economic slowdown. So the Dow Jones Industrial Average plunged 635 points, or 5.5%, to 10,810. The Nasdaq Composite index plummetd 175 points, or 6.9%, to 2,358. And the S&P 500 sank 80 points, or 6.7%, to 1,120. All ten economic sectors ended lower for the day, led by financials, industrial, materials and energy sectors. All thirty Dow components ended the day in the red. Bank of America led the Dow decliners, slipping almost 20%. The stock slipped after the The New York Times reported that American International Group plans to sue Bank of America in a bid to recoup more than 10 billion dollars in losses on mortgage-backed securities.