By now, it’s clear that the Israeli-Palestinian conflict is driving a rift into progressive, liberal, and Democratic Party ranks that may be as deep as the one caused by the Vietnam War. Whether it will be as lasting as the divisions of the ’60s remains to be seen. What is clear now, however, is that the political consequences this time around may be much more severe. Absent the Vietnam War, Hubert Humphrey would probably not have lost the 1968 presidential election to Richard Nixon. In a Biden-Trump contest next year, Israel-Palestine could be one more nail in the Democrats’ coffin....