Experts who track hate groups across the U.S. are growing increasingly concerned over violent rhetoric targeted at President Obama, especially as the debate over health care intensifies and a pattern of threats emerges. The Secret Service is investigating a Maryland man who held a sign reading "Death to Obama" and "Death to Michelle and her two stupid kids" outside a town hall meeting this week. And in New Hampshire, another man stood across the street from a Presidential town hall with his gun on full display. Los Angeles police officers apprehended a man Thursday after a standoff with him inside...