Hillary Clinton celebrates as her husband, former president Bill Clinton, kisses their daughter, Chelsea, at a rally in Des Moines. (Adrees Latif/Reuters)

To return to this state for another primary with a Clinton on the ballot is to be reminded about how much has changed in Democratic politics over the past two-plus decades and how much remains the same.

The change reflects the party’s evolution — or maybe its reversion to type — since Bill Clinton ran here in 1992. The sameness involves the Groundhog Day nature of Hillary Clinton’s challenge, selling pragmatic experience over alluring hope, against Bernie Sanders now as against Barack Obama in 2008.

Bill Clinton’s pitch, after Democrats’ long exile from the White House, was that he represented a third-way Democrat championing streamlined government and individual responsibility.

“We offer our people a new choice based on old values. We offer opportunity. We demand responsibility,” Clinton said in his 1992 convention speech. “The choice we offer is not conservative or liberal; in many ways it’s not even Republican or Democratic.”

How quaintly post-partisan that sounds in the hindsight of 24 years, when the different kind of Democrat running in 2016 is not, technically, a Democrat at all, but a self-described democratic socialist.

Indeed, the raging argument last week between Bernie Sanders and Hillary Clinton reflected the opposite impulse of Clinton 1992 — not who is the different-est Democrat but who is the most traditionally progressive one. Clinton bristled at what she described as the Vermont senator’s “low blow,” questioning whether she was merely a part-time progressive; the Clinton campaign scrambled to explain away her September self-assessment as a “moderate.”

Pause to consider the irony. Clinton has spent much of the past few decades trying to refute suggestions that she is a shade to the right of Madame Mao; recall Pat Buchanan’s 1992 GOP convention speech railing against her as a radical feminist who wanted to let children sue parents and compared the institution of marriage to slavery.

This is a tempting and dangerous moment for Democrats. The party has clearly become more liberal, reflecting the increasing polarization of both sides. According to the Pew Research Center, 41 percent of Democrats described themselves as liberal in 2015, compared with 27 percent in 2000. The share of Democrats identifying themselves as moderate fell from 43 percent in 2000 to 35 percent in 2015.

The success of Sanders’s full-throated progressivism among the party faithful is no surprise, especially in liberal-leaning Iowa and New Hampshire. But, notwithstanding the current head-to-head polls that he likes to cite, Sanders at the top of the Democratic ticket threatens a general-election disaster, and not just for the top spot.

True, more Americans overall identify themselves as liberal — up from 17 percent in 1992 to 24 percent in 2014, according to Gallup. But that leaves the vast majority with a different outlook, 34 percent who describe themselves as moderate, 38 percent conservative. How, exactly, are they going to respond to a democratic socialist’s call for a political revolution?

Sanders’s answer is that he could inspire a grass-roots revolution, producing a flood of new voters, as he said in Thursday’s MSNBC debate. I’m all for new voters, but I worry — and, more to the point, Democratic officeholders worry — about what happens when the Republican onslaught is unleashed against the essentially unknown, unvetted Sanders.

Revolution is easy to promise but hard to achieve in the current political environment and in the short space of a single campaign.

Which brings me to the striking way in which the 2016 argument echoes that of eight years ago. At the final pre-primary debate back then, Clinton was making precisely the same case: Change is hard. Achieving it requires more than impassioned rhetoric. She has proved her capacity to do so.

Consider this Clinton quote from the final debate before the 2008 New Hampshire primary: “What we’ve got to do is translate talk into action and feeling into reality. I have a long record of doing that, of taking on the very interests that you have just rightly excoriated because of the overdue influence that they have in our government.

“And, you know, probably nobody up here has been the subject of more incoming fire from the Republicans and the special interests. So I think I know exactly what I’m walking into. And I am prepared to take them on.”

No one could blame Clinton for feeling nostalgic for the party her husband led, or a sense of frustrated deja vu about the argument she seems endlessly condemned to make.

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