In a recent Washington Post op-ed, left-wing activist Steve Rosenthal sounds a lot like other wishful thinkers arriving at a comfortable partisan conclusion. America, he writes, is only a few years from a full-blown progressive electorate. "A close examination of U.S. attitudes in the past decade-plus," Rosenthal contends, "reveals that the United States is steadily becoming more progressive."

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.

In the end, the progressive agenda demands that you trust the state to control economic outcomes—an idea that is yet to be proved especially popular among Americans. Will it be? Who knows? But right now, what does seem to be growing is skepticism toward government, especially among the young. When Gallup asks about what people "think the most important problem facing this country today is," it doesn't bode well for the left that a plurality of people—independents, Republicans and Democrats—say it's government. Fifty-three percent of Americans claim to believe government does "too many things." (Forty percent think its powers should be expanded.) Add to this the fact that according to Gallup, a record number of Americans (42 percent) are rejecting partisan labels and identifying as political independents. Sounds as if there's a growing number of voters with a libertarian disposition—though most would never articulate it that way.

And right now, the unpopularity and struggles of Obamacare—the most notable political accomplishment associated with the progressive left—make it tough to imagine any electorate signing off on another national technocratic adventure in the foreseeable future. The Obamacare debate has made it nearly impossible to do anything in Washington (a triumph for libertarian governance). Judging from the polls, the voters Rosenthal claims are turning hard left seem to be more amenable to supporting reforms that loosen, rather than expand, federal control over health care. What makes anyone believe a more progressive alternative would be popular?

But like many folks on the left, Rosenthal is forced to make a big leap. He contends that a shift on social issues and the electoral success of (a now-unpopular) Barack Obama prove that the entire progressive buffet is destined for widespread approval. Guess what. It doesn't work that way. Support for gay marriage does not mean support for unions. (Unions, one of the backbones of political progressivism, have never been less popular in practice.) Pot legalization does not mean we're ready to nationalize energy policy. And support for immigration reform doesn't mean people are prepared to "make everything owned by everybody" as a writer in Rolling Stone suggests. And though I certainly don't believe we're about to privatize Social Security, to believe that the philosophy of the electorate is on a fixed leftward arc—which seems to be conventional wisdom these days—is premature.