Every presidential candidate would like to think that his supporters aren't just a bunch of disconnected people who happen to have chosen him for their vote, but rather an actual movement, a cohesive and powerful entity motivated by righteous impulses and capable of bringing change through its passion and toil. The more sweeping the change they demand, the more it seems like a movement. Right now, Bernie Sanders is the one who most often refers to his campaign that way, but others would like to claim it, too. Even Donald Trump, perhaps the most narcissistic individual ever to run for president, has said, "This is a movement... I don't want it to be about me."

That's what is supposed to define the campaign-as-movement: The candidate may be its leader, but it's really about something larger than him. But while campaigns can be inspiring, extraordinary things, they aren't movements. And if you're hoping that your candidate's campaign is really a movement that will reach beyond his or her election, you're probably going to be disappointed.

To understand why, we have only to look back on Barack Obama's 2008 campaign, probably the most extraordinary one you've seen in your lifetime. It saw new levels of engagement from all kinds of people, particularly young people, using innovative tools to spread the message and bring in new members.

Part of Obama's rhetorical genius was to make the participants in his campaign feel like they were creating history. "On this January night," he told them when celebrating his victory in the Iowa caucus, "at this defining moment in history, you have done what the cynics said we couldn't do." Then, sounding like Shakespeare's Henry V at Agincourt, he went on: "Years from now, you'll look back and you'll say that this was the moment — this was the place — where America remembered what it means to hope." For people who had spent much of their lives up until that point as spectators, watching history play out on television, it was extraordinarily powerful to think of themselves as the ones actually creating epic events.

But for all Obama talked about "you" and "we," in the end his movement really was about him — or rather, the very specific goal of getting him elected. There was an attempt to transform the remarkable campaign into a semi-permanent movement — Obama for America became Organizing for America and was folded into the DNC, then after 2012 it was followed by Organizing for Action, all of which was intended to keep the energy of the campaign alive through his administration. But even though the people involved will tell you about all the phone calls they've made or doors they've knocked on in support of various administration initiatives, it has been a struggle — and one that has always paled in comparison to what Obama's two campaigns managed to create.

That's because campaigns are unlike movements in some crucial ways. The contained and finite nature of a presidential campaign is what allows organizers to be so effective within it, to in a matter of months go from nothing to a nationwide effort involving hundreds of employees, thousands of volunteers, millions of contributors, and tens of millions of voters. It's because it has a clear goal, a deadline on which victory or defeat will be known, and obviously high stakes. When you join it, you're participating in the exciting enterprise the whole country is focused on.

But once the campaign is over, only a core of committed activists are going to continue working. And when they have to clarify a new agenda — as opposed to "Get our guy elected" — it can prove not as engaging or inspiring for many, who will move on to other things. As for Obama, he found that the hard slog of governing, full of compromises and setbacks, drained away much of that idealistic energy.

None of the truly transformative movements in recent history, like those for civil rights or gay rights, grew up out of a presidential campaign; instead, they started from below and ended up pulling politicians along with them.

Think back on recent presidents: Which ones would you really say led a movement? Was there a Bush movement or a Clinton movement that transcended those presidents themselves? Even Ronald Reagan, lionized as he is by conservatives today, didn't truly lead a movement that was larger than him. He managed to get a plethora of conservative movements to unite behind his campaigns, but, just like Obama, he disappointed many of his followers (who by now have convinced themselves to forget that he raised taxes, didn't outlaw abortion, and ballooned the deficit).

It's obviously desirable to have a campaign that carries the flavor of a movement, with a sense of destiny and passionate supporters who'll work their hearts out for the cause. If anyone has that right now, it's Sanders. But that only goes so far, and much of the time it peters out, as it did for candidates like Howard Dean.

Barack Obama these days sounds much more pragmatic about presidential politics than he once did. In a recent interview with Politico, he said, "Bernie has tapped into a running thread in Democratic politics" that looks for transformational change, "And, you know, that has an appeal and I understand that." But he then offered this: "I think that what Hillary presents is a recognition that translating values into governance and delivering the goods is ultimately the job of politics, making a real-life difference to people in their day-to-day lives."

In other words: It's great if your campaign feels like a movement, but for better or worse, that won't solve the problems being president presents.