I used to believe a third party that positioned itself as centrist could be viable, potentially enough to actually govern at some point. Centrist, "sane" candidates have a very hard time winning primaries in the two-party system. A third party could have its own primary process, and if it somehow could get enough attention and dollars, you would think it could, or at least should, work. Most Americans want similar things ... e.g., centrist Democrat policies from the 90s/early 2000s. No, not denying science, trying to make America a theological nation, or meritless armed conflict, as more extreme Republicans of that era did. Not about cutting taxes to the bone, running huge deficits to spend on defense, and so on. But also not trying to frame everything in identity group politics or going way out on the tail of extreme policies regarding myriad issues (e.g., the border, illegal immigration, policing and safety, DEI, transgender matters, censorship, abortion, court-packing, reparations, and various other things), many of which wouldn't have even had majority support in places like Berkeley in that era.
Things have gotten so extreme, with apparent disagreement over things that shouldn't be all that controversial--each day is so insane with the news flow that I can't discern whether this is just election-related posturing or something indicative of greater partisan divergence--that it no longer is clear to me the sizeable, silent, largely apolitical middle who just wants things that make sense could ever come together to get it done.
The media also is a massive problem. It has leaned left at least for the past six decades, and it was Murdoch who first created the current-day polarized talking head shitshow with Fox, of course, but the left-leaning cable outlets at this point are just as bad if not worse, and the legacy MSM isn't far behind. This contributes to further demonization of the other side and polarization, and no centrist, dispassionate media outlet ever is viable despite a few attempts to start them over the years. What gets viewed, consumed, and ads purchased is extreme bullshit on both sides, blasted out to political obsessives who lap it up.
Try looking at the "other side's" material for a little bit on social media. You'll find it repugnant at a visceral level, yes, and I can barely do it on either side, but gut through it for a few minutes and realize how the same world is portrayed completely differently. Balanced views simply aren't presented. Facts that don't support that side's narrative, which at this point is just that the other side is abhorrent, corrupt, and will put you in camps and ruin the country, regardless of which side you are on, aren't reported even if they are merely neutral or clarifying. There is no place for moderates, even though they probably still represent a plurality in this country. They are left to try to look at the ridiculous shit from both sides and trying to discern truth from caricatures and absurdity.
That probably will piss off everyone, which itself would be telling vis-à-vis the viability of centrists now and going forward.