Liberal firebrand Michael Moore called on President Obama to respond to the U.S. credit downgrade by arresting the leaders of the credit-ratings agencies. On his Twitter feed Monday, the Oscar-winning film director also blamed the 2008 economic collapse on Standard & Poor’s — apparently because it and other credit-ratings agencies did not downgrade mortgage-based bonds, which encouraged the housing bubble and let it spread throughout the economy. “Pres Obama, show some guts & arrest the CEO of Standard & Poors. These criminals brought down the economy in 2008& now they will do it again,” Mr. Moore wrote. Standard & Poor’s,...