Can diplomatic optimism hold until U.S. markets reopen?US500BLACKBULL:US500BlackBull_MarketsEuropean stocks are responding to improving diplomatic signals between Washington and Tehran. The Euro STOXX 50 and broader STOXX 600 are both back within reach of their late February record highs. Germany’s DAX rose to its highest level in more than four months. Italy also stood out, with the FTSE MIB briefly touching an all time high of 50,114 before giving back part of the move. The next test comes when U.S. markets reopen after the Memorial Day closure. Monday’s move showed that investors are willing to buy European equities when energy risks ease. A lot can happen in the next 12 hours before U.S. markets open. Diplomatic progress may become something more concrete or disintegrate as it has many times before.