Democratic presidential candidate Sen. Bernie Sanders, I-Vermont, has a 6 p.m. rally at Williams Arena on the U campus. Sanders, above, spoke at the Minnesota State Fair in August. (Star Tribune/The Minnesota Star Tribune)

The Democratic Party needs a nominee, but right now it has a train wreck instead. The front-runner seems too old for the job and is poised to lose the first two primary season contests. The woman who was supposed to become the front-runner on the basis of her policy chops is sliding in the polls after thoroughly botching her health care strategy. The candidate rising in her place is a 37-year-old mayor of a tiny, not-obviously-thriving city.

Meanwhile several seemingly electable alternatives have failed to catch fire; the party establishment is casting about for other options; and not one but two billionaires are spending millions to try to buy delegates for a brokered convention … which is a not-entirely-unimaginable endgame for the party as it prepares to face down Donald Trump.

The state of the Democratic field reflects the weaknesses of the individual candidates, but it also reflects the heterogenous nature of the Democratic coalition, whose electorate has many more demographic divisions than the mostly white and middle class and aging GOP, and therefore occasionally resembles the 19th-century Hapsburg empire in the challenge it poses to aspiring leaders.

The theory of the Kamala Harris candidacy, whose nose-dive was the subject of a withering pre-mortem from three of my colleagues over Thanksgiving, was that she was well suited to accomplish this unification through the elixir of her female/minority/professional class identities — that she would embody the party's diversity much as Barack Obama did before her, and subsume the party's potential tensions under the benevolent stewardship of a multicultural managerialism.

That isn't happening. But it's still reasonable for Democratic voters to look for someone who can do a version of what Harris was supposed to do, and build a coalition across the party's many axes of division.

And there's an interesting case that the candidate best positioned to do this — the one whose support is most diverse right now — is the candidate whom Obama allegedly promised to intervene against if his nomination seemed likely: the resilient Socialist from Vermont, Bernie Sanders.

Like other candidates, Sanders' support has a demographic core: Just as Elizabeth Warren depends on very liberal professionals and Joe Biden on older minorities and moderates, Bernie depends intensely on the young. But his polling also shows an interesting better-than-you-expect pattern, given stereotypes about his support. He does better-than-you-expect with minorities despite having struggled with them in 2016, with moderate voters and $100K-plus earners despite being famously left-wing, and with young women despite all the BernieBro business.

This pattern explains why, in early-state polling, Sanders shows the most strength in very different environments — leading Warren everywhere in the latest FiveThirtyEight average, beating Biden in Iowa and challenging him in more-diverse Nevada, matching Pete Buttigieg in New Hampshire and leading him easily in South Carolina and California.

Now, I have stacked the argument slightly, and left out a crucial axis of division where Sanders does worse than you expect: He struggles badly with his fellow Social Security recipients, the over-65. This weakness and Biden's strength with these same voters are obvious reasons to doubt the case for Bernie as the unifier, Bernie as the eventual nominee.

Especially since Sanders has thus far ignored my advice (I know, the nerve) that he reassure skeptics by telling them that he has a record as a dealmaker, that he can moderate on certain issues, so they can feel safe supporting him even if they aren't ready for the revolution.

But still: If you are a wavering Democrat concerned about both party unity and ultimate electability, about exciting all the diverse factions of your base while also competing for the disaffected, both the relative breadth of Bernie's primary coalition and his decent polling among non-voters and Obama-Trump voters are reasons to give him another look.

That decent polling, I suspect, reflects a sense among voters drawn to populism that Bernie is different from not only the more centrist candidates — latecomers Michael Bloomberg and Deval Patrick especially, but Buttigieg as well — but also from his fellow left-winger, Warren, who has fully embraced the culture-war breadth of the new progressivism while Sanders remains, fundamentally, an economic-policy monomaniac.

He's still a social liberal, of course, and he isn't in the culturally conservative/economic populist quadrant where so many unrepresented voters reside. But for the kind of American who is mostly with the Democrats on economics but wary of progressivism's zest for culture war, Sanders' socialism might be strangely reassuring — as a signal of what he actually cares about, and what battles he might eschew for the sake of his anti-plutocratic goals. (At the very least he's no more radical on an issue like abortion than a studied moderate like Mayor Pete.)

This is why, despite technically preferring a moderate like Biden or Amy Klobuchar, I keep coming back to the conservative's case for Bernie — which rests on the perhaps-wrong but still attractive supposition that he's the liberal most likely to spend all his time trying to tax the rich and leave cultural conservatives alone.