Bernie Sanders's stunning rise is giving veterans of Hillary Clinton's 2008 campaign an uncomfortable sense of déjà vu. That déjà vu, of course, comes from their collision with Barack Obama's 2008 campaign. But what about veterans of Obama's 2008 campaign? What do they see in Sanders's momentum?

"He’s better than anybody realized," says David Axelrod, who served as Obama's chief strategist in 2008. "There is a rumpled authenticity to Bernie Sanders that really resonates, particularly with young people who have finely tuned bullshit meters."

Sanders's slogan — "A future you can believe in," plastered over a dark blue background — is nearly plagiarized from Obama's "Change you can believe in." His record-breaking small-donor haul builds on Obama's small-donor success in 2008. His numbers among young Democrats are even better than Obama's were. And his packed rallies are proof of the hope he's restored in liberals — hope that a different kind of politics is possible, that a different kind of candidate can win, that the boundaries of American politics are not what we thought.

In conversations with veterans of the Obama campaign both the day before and the day after the New Hampshire primary, their assessment of Sanders mixed real admiration with genuine dismay. They recognize the excitement Sanders is generating among Democratic voters — including groups they had trouble reaching, like white voters with incomes under $50,000. And they recognize that in some ways, Sanders is climbing an even harder hill than Obama did in 2008.

"Both candidates ran from the outside, but Obama had significant establishment support in his campaign, including from the traditional Democratic donor base," says Anita Dunn, a senior adviser on Obama's 2008 campaign. "Sanders's fundraising is all the more remarkable because he will not get the high dollar-donors that Obama did."

But, in a reaction that may reflect the experience of Obama's presidency as much as his campaign, the Obama veterans are almost universally frustrated by Sanders's message, which they see as both less realistic and less unifying than what they offered in 2008.

"Obama got in the race to be president, and Sanders got in the race to send a message, and you can see that difference in their approaches to policymaking," says Dan Pfeiffer, who was Obama's communications director in 2008. "Obama wouldn't support a policy unless he felt it was feasible if he was president. Sanders doesn't seem to have that limitation, which gives him more message purity and a sharper contrast with Clinton, but is a huge substantive and political problem if he ends up in the White House."

There's something to this — whereas Sanders countered Clinton's 2016 health care plan with single-payer, Obama countered Clinton's 2008 health care plan with a more modest plan. In broad strokes, Obama's policy platform in 2008 channeled the mainstream of the Democratic Party, while Sanders's 2016 platform is trying to pull the party much further to the left. But it's worth noting that Obama also made plenty of promises, particularly on process, that proved fantastical, like leaving the health care negotiations open to C-SPAN or keeping his administration entirely free of former lobbyists.

Still, there are ways in which even Obama's process promises were more incremental than Sanders's. Jon Favreau, Obama's speechwriter on the 2008 campaign, points to a line Obama used often on the trail, where he would say, "It's time to let the drug and insurance industries know that while they'll get a seat at the table, they don't get to buy every chair." Over email, Favreau unpacked its importance:

To me, this exemplifies the difference between Bernie and Obama. Bernie would never say something like that. He doesn't think insurance companies, or drug companies, or banks, or millionaires get any seats at the table. He doesn't talk about making progress by working with Republicans, or the political establishment, or the business establishment. I guess his plan is to build a mobilized grassroots that simply wrestles power away from those who have it. It's not just that Obama doesn't think that's feasible, it's that he doesn't think that's the right way to govern in a pluralistic democracy where everyone gets a voice. Obama believes that there's too many Americans who don't have a voice, and too many Americans who don't have opportunity, and that a big reason for that is the power of special interests and big corporations. But he also believes that there's a place for those interests and corporations in our system.

For these reasons, veterans of Obama's 2008 campaign rankle at the comparisons made between their candidate and Sanders. Yes, both were transformational candidates running on a promise to change American politics. But Obama's ex-staffers see the campaigns as quasi-opposites.

"The Obama-Sanders comparisons are overly facile," Pfeiffer continues. "In 2008, Obama's campaign was about channeling hope, and Sanders's is about channeling anger — well-deserved, righteous anger, but anger nonetheless."

In this telling, the core difference between Obama and Sanders is that Obama's theory of political change was that American politics needed to become less ideological and less conflictual, while Sanders's theory of change is that American politics needs to be made more ideological and more conflictual. Obama thought a better, more technocratic, more generous process would reveal a larger space for compromise, while Sanders thinks a more sharply defined platform will reveal that there's less need than anyone thought for compromise.

"The campaigns are different," Axelrod says. "Obama’s was not really an ideological campaign. There was a big difference on the war, but Obama was not the candidate of the left. John Edwards was the candidate of the left in Iowa. The left was often suspicious of Obama because of his approach, which is, '80 percent is better than nothing.'"

"The assumption that Sanders has," Axelrod continues, "is that the American people support his positions on every issue and if you just move money out of the way, those positions would prevail. On a question like single-payer, that’s not true. I support single-payer health care, but having gone through health reform, we couldn’t even get a national consensus around the public option! It was Democratic votes that were ultimately missing on that issue."

This is a place where the Obamaites, looking back, feel that Obama's message was often misunderstood — his optimism sometimes masked his incrementalism.

"Obama promised change," Dunn says, "not a revolution."