It seems to be widely accepted by the media that demographics, GOP ineptitude and internal division, and a generational shift on social issues place the American voter on an enduring leftward course. Is this inevitable? Well, about as inevitable as Karl Rove's durable Republican majority.
You don't have to be a stickler for academic rigor to appreciate that an 825-word column with a few links to some Gallup polls is not really a "close examination" of anything. But you don't have to be a historian to understand that the electorate, though hardly immune to terrible ideas, is, in the end, stubbornly moderate with little use for philosophical consistency. Which is to say, no one knows what the future will look like.
Voters not only have conflicting ideological views but also change their minds on those issues all the time -- and oftentimes for no good reason at all. We are irrational. We are mercurial. We're irresponsible. And when we're not, events that "change everything" (9/11 and the Great Recession come to mind) tend to blow up these alleged electoral trajectories we're on anyway. And let's not forget voter backlashes, religious awakenings, economic booms and busts, political scandals, charismatic leaders, and technological advances, all of which can disrupt lines on the graph.
That's just broadly speaking, of course. Even if we accepted Rosenthal's facts in the short term, a person could use his piece to make a rather compelling case that the nation is trending more libertarian than it is progressive.
A cultural shift is not always an ideological one -- or at least not always the one you imagine. Our norms are always evolving. Immigration, pot legalization, same-sex marriage and "big business" are the issues that Rosenthal claims portend progressivism's triumph. Yet most of these are only incidentally progressive. Marijuana legalization or support for same-sex marriage is far more likely caused by a growing "live and let live" mindset than it is any burst of leftist idealism. And if the "live and let live" mindset starts bleeding into other areas of American life -- say, education, health care and religious freedom -- the left is in trouble.