(CNN) Hillary Clinton is not running for president in 2020.

And yet, Clinton is, again, at the center of a four-year-and-counting civil war within the party she represented in the 2016 general election -- a fight for the future of Democrats that will begin to be decided in 24 hours' time in Iowa.

The latest flare-up came Friday night, when Michigan Democratic Rep. Rashida Tlaib, an outspoken liberal and supporter of Bernie Sanders, booed the mention of Clinton at a rally for the Vermont senator.

"No, no, I'll boo," Tlaib said. "You all know I can't be quiet. No, we're going to boo," she said. (Tlaib later apologized via Twitter.)

Tlaib's booing came after a series of attacks by Clinton on Sanders for not only the race he ran in 2016 but also the way in which he is viewed by his peers.

"He was in Congress for years," Clinton said in a new documentary of her campaign. "He had one senator support him. Nobody likes him, nobody wants to work with him, he got nothing done."

Then, on Friday, Clinton said this on the "Your Primary Playlist" podcast:

"All the way up to the end, a lot of people highly identified with [Sanders'] campaign were urging people to vote third-party, urging people not to vote. It had an impact."

What's interesting about all the back-and-forth is that both sides have a legitimate gripe!

There's no question that, while Sanders ultimately did endorse Clinton's campaign, he did so slowly and begrudgingly. And that, even after he had thrown his support behind her, many of Sanders' most ardent backers never really got on board with Clinton.

And that lack of enthusiasm likely did play some role in her defeat. (Where I diverge from Clinton, however, is in her willingness to lay much of the blame for her loss at the feet of Sanders' supporters. She didn't lose to President Donald Trump because of that factor. No way.)

From the Sanders perspective, it's hard to not want to push back against Clinton saying that the Vermont senator has no friends and cost her the election. While Tlaib's booing may not have been the perfect response, you can understand the frustration among the left toward Clinton, who not only lost what everyone in the Democratic Party assumed was a slam-dunk election in 2016 but has spent the last 3+ years blaming everyone but herself for it.

What's most remarkable about all of this is not that it's happening -- presidential nomination fights should (and almost always are) key inflection points over who a party is and where it's going -- but that the catalyst of the whole shebang is a candidate who isn't even running for office (and likely never will again).

To be clear: The divide Clinton is highlighting between liberal crusaders and establishment pragmatists very much exists in this current nomination fight. Sanders is, again, carrying the torch for liberals while Joe Biden (and, to a lesser extent, Pete Buttigieg and Amy Klobuchar) are seen as the pragmatic candidates.

But there's been next-to-no engagement between the two factions of the party. Sure, Sanders has suggested Biden has been on the wrong side of lots and lots of key issues for the party (NAFTA, Iraq war, etc.). And yes, Biden has taken to noting that Sanders isn't a "real" Democrat of late.

It's all been done, however, with the lightest of touches -- as though none of the candidates are really willing to take a hard swing for fear of what might happen if it fails to connect. The lack of tough contrasting could well change after Monday night, when we have a clearer sense of who is on top and who, well, isn't. That's been difficult to ascertain to date because of the decidedly wide-open field.

Don't mistake a lack of willingness to draw contrasts with a lack of contrasts, however. The Democratic Party that will offer up its presidential choices to Iowa voters on Monday night is deeply riven over any number of major questions from health care delivery to economic policy to, and perhaps most importantly, how much (or little) Trump has changed American politics.

Clinton's central role is the oddity here. In trying to re-litigate how she lost in 2016, she is forcing a conversation -- or at least a confrontation -- within the Democratic Party about what it is and what it should be.

Once voters vote -- and we have less than 24 hours to wait! -- we will begin to get answers the very questions Clinton is pushing to the fore.

"The haters will shut up on Monday when we win," Tlaib predicted.

I somehow doubt it.