{video} The leaders of Corporate America are cashing in their chips as doubts grow about the sustainability of the longest bull market in American history. Corporate insiders have sold an average of $600 million of stock per day in August, according to TrimTabs Investment Research, which tracks stock market liquidity. August is on track to be the fifth month of the year in which insider selling tops $10 billion. The only other times that has happened was 2006 and 2007, the period before the last bear market in stocks, TrimTabs said. Investors often view insider buying and selling — transactions performed by top ... (full story)