For years, a growing stripe of Democrats has argued that what their party needs is a leader willing to shatter old assumptions, a radical disrupter. Well, Democrats already have found their transformational figure for the 2020 campaign. His name is Donald Trump.Story Continued Below No one could miss the obvious ways this president—despite his deviations from traditional conservative orthodoxy—has turned the Republican Party into the pro-Trump party. It could be easy to miss, however, some of the less-obvious ways Trump also has made himself the defining force of the anti-Trump party. All presidents tend to reshape the politics of their era, sometimes in ways that long outlast their time in office. JFK’s mastery of television infused once-dowdy progressive politics with a measure of glamour that politicians spent decades emulating; Reagan’s success in using well-turned anecdotes and homilies to drive a conservative movement shapes the presidency to this day. It is striking, though, how true this has been even in the 2020 Democratic primary, in which the competition is over which candidate can most credibly claim that he or she will not just beat Trump but repudiate all he stands for. On stylistic and even substantive grounds, Trump is arguably exerting…