(AP Photo/Brynn Anderson)

As Iowa comes down to the wire, the parallels to the 2008 battle between Hillary Clinton and Barack Obama are striking. Clinton has reverted to a hard-boiled message about the need for experience and toughness to confront a dangerous, complicated world.

Meanwhile, Bernie Sanders is increasingly sounding an optimistic, inspirational message that promises a bright, progressive future that can, and will, be secured through mobilizing the masses, particularly younger voters, a vision that Clinton surely sees (just as she saw Barack Obama’s vision) as vague, airy, and naive.

Sanders is up with this remarkable new ad in Iowa whose tagline — “a future you can believe in” — conspicuously echoes Obama’s 2008 “change you can believe in” formulation:

Democratic presidential candidate Bernie Sanders released a new campaign ad titled "America." Paul Simon's song "(All Come To Look For) America" plays over scenes of rural and suburban America. Sanders appears nearly halfway into the ad greeting crowds at a rally. (Bernie 2016)

In a way, this ad perfectly captures Bernie Sanders’ theory of change, or at least, a version of it that has had its more pessimistic or even apocalyptic edges airbrushed away to make it easier on the eyes and ears. Hence the dulcet tones of Simon and Garfunkel’s “America,” which tells a tale of young lovers on a road trip, suffusing this ad with an odd mix of nostalgia (this song was recorded in the late 1960s, when Sanders and Clinton were both in their twenties) and idealism about the future.

The Sanders argument, to put it simply, has essentially been that America is in deep, deep trouble — it faces structural challenges so pressing and urgent, from climate change to soaring inequality, that the failure to meet them with proportionately outsize solutions risks a slow motion slide into disaster that could prove irreversible. Sanders’ message has been that the version of progressive change that we’ve seen during the Obama years — from Dodd Frank to Obamacare to the global climate deal — is basically small beer compared to the epic problems we face. That’s what makes this new ad so striking: it doesn’t detail these challenges, instead suggesting vaguely that inspiration and mobilization can secure America’s future.

Sanders has discussed his theory of change on multiple occasions, in ways that capture this tension between pessimism and urgency about the depth of our challenges and optimism that people-power can meet them, regardless of our political system’s structural impediments to the sort of change Sanders seeks. In a recent interview with Vox, Sanders was asked how, given GOP control of Congress, he would realize goals such as single payer, far reaching climate policies, much higher marginal tax rates on the very wealthy, reforms that would break the hold of big money over our politics, and so on. He responded:

“The real way that change takes place — and that’s always been the case in this country — is when people on the bottom begin to stand up and say enough is enough. That’s true of the civil rights movement, it is true of the women’s movement, it’s true of the environmental movement, of the gay movement. Millions of people begin to stand up and say, ‘We need change. Current situations are intolerable.’ That is when change takes place….

“I believe we can rally the American people, tens of millions of people, to say, ‘You know what? The United States Congress is going to start listening to us and not to a handful of wealthy campaign contributors.'”

Sanders has also said: “The major political, strategic difference I have with Obama, is it’s too late to do anything inside the Beltway. You gotta take your case to the American people, mobilize them, and organize them at the grassroots level in a way that we have never done before.”

This theory of change is perhaps unrealistic, given the structural realities of how our political system works and of the GOP grip on the House of Representatives. It may not be sufficiently nuanced to do justice to the lessons of our history: major change has arguably been won both from the outside and the inside. It has sometimes been the product, in part, of very ugly exercises of inside manipulation, dealmaking, logrolling, bullying, and ethical corner-cutting, and has required not just inspiration, but fighting, bloodshed, and death.

To be clear, it’s indisputably a good thing that Sanders is setting the policy bar very high. That’s great for the debate, and has made the Democratic primary deeply substantive and has forced Clinton to be a better candidate and offer more ambitious proposals than she otherwise might have if she had followed only her own instincts. And Sanders’ success in energizing young people and, hopefully, engaging them more deeply in the process is a big positive and should alarm Clinton and get her to take notice.

Still, it’s worth noting that the differences between Sanders and Clinton go beyond policy, to the very core of how change can be secured. Clinton has come to see politics as essentially a form of trench warfare. Clinton’s closing ad in Iowa vows to “stop the Republicans from ripping all our progress away,” an implicit acknowledgment that a new Democratic president (whoever it might be) would be deeply constrained from realizing his or her agenda, meaning the 2016 election is mostly about whether Dems can prevent total Republican rule from rolling back the gains of the Obama years. Clinton acknowledges the true nature of the structural impediments to change; that the country is deeply divided ideologically; and that we will probably remain stuck in a grueling holding pattern for years — meaning legislative advances will be ground out on the margins, thorough difficult, painstaking efforts to peel off Republicans and forge compromises that will look dirty and will really, really suck.

That’s not very inspirational, but it’s probably accurate — dispiritingly so, in fact. Meanwhile, Sanders wants people to feel swept up in a movement.