Jill Filipovic is a journalist based in New York and Nairobi, Kenya, and the author of the book " The H-Spot: The Feminist Pursuit of Happiness ." Follow her on Twitter . The opinions expressed in this commentary are solely those of the author.

(CNN) There are few things more unpleasant than relitigating the 2016 Democratic primary. But more than a year later, it hasn't stopped, partly because the race touched on so many hot spots that continue to animate our politics: the way gender shapes how we perceive power, how class struggle collides with racial entitlement, what it even means to be "progressive" or to work outside the system.

And now, there's something new to argue over: Hillary Clinton's forthcoming book, "What Happened."

In it, according to excerpts posted by a group of Clinton supporters, she criticizes her primary opponent , Bernie Sanders, for running to be the Democratic nominee while not actually being a Democrat, and for targeting her in a campaign of character assassination, instead of doing a deep dive into policy.

Predictably, the response from the Sanders left and the Trump right has been about the same: Shut up and go away. This is after the demands that she "take responsibility" and "apologize." (Has any politician in the history of America been ordered to say she's sorry as often as Hillary Clinton?)

Is the relitigation of the primary pleasant? No. Is a look at what happened, from the perspective of the only woman in American history to be a hair's width away from the presidency, a pretty valuable contribution? Yes.

And while this will certainly take a few minutes away from a news cycle of North Korean nukes, horrific natural disasters and a growing list of Trump cruelties and blunders, there isn't really a better time: In a few months we'll be gearing up for the midterm elections, and after that, our insane election cycles will have us in presidential-campaigning mode. It seems likely that Sanders will again be one of the campaigners.

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And so it's only fair to take a look at his previous efforts, and learn some lessons. Clinton is right: Sanders' attacks on her character fed the same narrative as Trump's. They hurt her in the general election. And she's right that running on the Democratic ticket when you're not a Democrat isn't just hypocritical, it can be incredibly damaging. For one thing, it gives a candidate a platform to trash the very party he says he wants to lead.

On the left today, the Sanders/Clinton divide remains. In some progressive circles, being a "neoliberal" is, as others have astutely observed , "the left's favorite insult," a handy catchall for everything that's wrong with the world. In their framework, Hillary Clinton is the epitome of neoliberalism, which is why she lost; Bernie Sanders is the bulwark against it, which is why he lost (funny how that works).

"Neoliberal" unfortunately remains ill-defined -- in theory it means a social liberal who favors global capitalism and corporate-friendly policies at the expense of social welfare; in practice, it seems to mean anything from "a member of the Democratic Party" to "anyone who voted for Clinton" to "someone I am simply deeming less progressive than me" to "a description of actual right-wing Republican-crafted policies that are somehow getting blamed on Democrats."

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This is because among some factions of the left -- Sanders loyalists, newly minted socialists -- being a liberal is just as bad as being an anti-gay pro-gun anti-choice tax-slashing administrative-state-dismantling deep-red congressman who moonlights as a Breitbart columnist.

Is that Sanders' fault? No. (And indeed, the ascendance of his brand of socialism in the United States is long overdue.) But his attacks on the Democratic Party helped set the stage for this thoroughly dysfunctional, and ultimately destructive discourse.

On the right, things are different. What's clear from the seeming millions of post-election dispatches from "Real America" (that is, working class white America; black and brown America somehow rarely makes the authenticity cut) is that a whole lot of conservative voters cast their ballots for Trump not because they share his values exactly, or because they were voting for anything, but because they hate liberals and wanted to give us the finger.

A sophisticated right-wing propaganda machine has helped to sow this malevolence, and the GOP has reaped the benefits.

Too much of the left has joined right in on the liberal-bashing. What too many on the left don't realize, though, is that the rest of the country — the nonleft -- doesn't make the distinction between liberals, progressives, socialists and so on. We're all just liberal elite scum. And that's why we're all losing -- from the far-left Bernie wing (whose policies I'm more inclined to support) to centrists (of whom Clinton, who ran the most progressive campaign in American history, was not exactly one).

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The 2016 primary pushed the Democratic Party further to the left than any time in its history. For that, Sanders deserves a lot of credit.

But the Democrats lost, and, as Clinton points out, Sanders also deserves some "credit" for that. The reasons behind Clinton's loss are many, and Sanders was hardly the No. 1 cause. But he was no neutral force.

The fact is, if those of us who want to move our country to the left are going to win -- not just elections, but on a policy level and a cultural one, too -- we need to stop buying the right-wing lines about liberals and Democrats, and stop demonizing our closest allies and best chances of retaking any power at all.

Sanders has positioned himself as a leader for the future of the left, and his followers agree, with near-messianic worship. Embracing the whole left would be a good place for him to start.