U.S. stocks opened lower Tuesday, joining a global equity selloff triggered by worries about a potential political crisis in Italy. The Dow was off 190 points, or 0.8% at 24,563. The S&P 500 fell 0.7% to 2,702, while the Nasdaq Composite dropped 0.5% to 7,399. Italy's president over the weekend blocked the formation of a coalition government, sparking expectations for new elections as early as this fall which analysts fear could turn into a de facto referendum on the country's membership in the euro.