Think of a senator winning the Democratic nomination in the year 2000 whose positions included halving the military budget, socializing the medical system, re-regulating the communications and electrical industries, establishing a guaranteed minimum income for all Americans, and equalizing funding for all schools regardless of property valuations — and who promised to fire Alan Greenspan, counseled withdrawal from the World Trade Organization, and, for good measure, spoke warmly of adolescent sexual experimentation. He would lose in a landslide. He would be relegated to the ash heap of history. But if the precedent of 1964 were repeated, two years later the country would begin electing dozens of men and women just like him. And not many decades later, Republicans would have to proclaim softer versions of those positions to get taken seriously for their party’s nomination.