After Donald Trump endorsed a Florida ballot initiative that would legalize recreational marijuana in that state, Kamala Harris accused her Republican opponent of flip-flopping on the issue. Yet the vice president herself did not publicly support marijuana legalization until 2018, when two-thirds of Americans already favored that policy. The truth is that both presidential candidates have changed their positions on this issue over the years, reflecting a sea change in public opinion. But that does not necessarily mean that either, if elected, would invest any effort in addressing the untenable…