Most economists believe that while the recovery remains fragile, it is likely to accelerate over the next year. As recently as a month ago, the American people agreed. But they don’t anymore. And there is a threat that these suddenly gloomy expectations could turn out to be perversely self-fulfilling—causing Americans to stop spending and investing, and thus hobbling the pace of economic growth to slow the already subpar job rebound.Two recent surveys highlight the shift in popular s...