I think all the people dumping on our chances in the civil war need to keep two things in mind:
1. So long as it takes place in the near future, it's not gonna be the left vs everyone else. The American socialists are simply too small and too powerless to actually fight the entire neoliberal establishment, and I think all the modern lefty orgs realize this and act accordingly (except the Revcoms, but they're insane cultists so I think we can disregard their "theory"). Rather, I think it's FAR more likely that an upcoming civil war would be similar to Spain's, with the reactionaries in power going mask-off (maybe through a coup or blatantly rigged election) and thus receive opposition from a brought range of socialists and progressives. Yes, it means that we'd have radlibs on our side, but it also means that we would be comparable in sheer numbers and strength. We could probably also expect significant foreign aid as well as mic defectors.
2. The forces of the left would consist of actual revolutionaries. Remember that these boog bois and militia types are mostly comfy larpers, people who are overall contented with the status quo besides a couple of idpol issues and "muh guns". They have very little of the GENUINE proletariat on their side, and most of their "populism" is just petit-bouj fantasy. Meanwhile, as much as we like to conceive of the American "left" as effeminate and disarmed, we have to also remember that such a civil war would almost certainly see us being joined by the black, Hispanic, Appalachian, Native American and Polynesian populations. These people, due to their long-standing oppression, have both the real incentive to overthrow the status quo as well as the lifetime of hardship to build a fighting force. These are people who were often imprisoned and forced to fight cops on a daily basis, they're going to be far more powerful than your average Kyle Rittenhouse. Organizations like the BPP and the AIM have already proven that they can form effective revolutionary forces despite being massively disadvantaged. I mean, remember that a small band of Native Americans in the 70s was able to hold out against the force of the US military. If we were to see boog bois and right-wing militias go up against the NABPP or the Huey Newton Gun Club, I think we all know that those "badass conservative patriots" would be pissing their pants and begging for mercy.
tldr; with a broad-enough progressive coalition and the support of the oppressed nationalities, I think the left could easily win a second civil war