Stocks fell on Wall Street Tuesday following their best weekly performance of the year as investors faced continued uncertainty in the wake of Britain's decision to leave the European Union and as tumbling oil prices weighed on energy shares."Brexit is a friction on economic activity and that's bad for banks," said Brian Battle, director of trading at Performance Trust Capital Partners in Chicago."Low interest rates are horrible for financials, specifically for banks. The spread between where they borrow and where they lend is getting closer together."