Everyone is speculating about Trump running 3rd party/independent if he doesn’t win the nomination. And the reason why they’re worried about that is because it would split the right wing vote giving the left an easy win. Splitting the democratic vote as well just removes the chance of an increased margin win, a mandate etc. And doing it without a similar split on the right just gives the GOP an easy win. Because of the polarized and partisan situation on the ground in this country. In national elections somewhere around 45% (a basic plurality whatever the exact number) of Americans simple vote Republican or Democrat automatically, and down the ballot. Regardless of platform, candidate or stakes. With somewhere less than 10% typically willing to branch out from that. You provide 2 candidates from the same end of the political spectrum for any one office, and you split up that reliable ~45%. ~22% give or take (rough stupid numbers I know) doesn’t give you a win when the other guy can still reliably take ~45% of the vote. Assuming huge numbers of people will switch to wholly change that dynamic ignores that those people genuinely disagree on politics. It would take a something massive to change that in a time span of months. Instead its changing slowly, as demographics change and the country is ideologically starting to shift left.
This election is in large part not about the presidency. Its about maintaining control of the the white house and senate, and waiting for or taking advantage of those changes. As it stands the GOP’s undemocratic, and disproportionate control of The House and many states counties etc. is what will (and does) allow them to stall out any legitimate progressive push. Regardless of who’s making that push. The Democratic nominee whoever they are, and how every far left they decide to go, is the only reliable way to make sure a conservative doesn’t end up in the white house and not just stall things out. But actually reverse gains that have already been made. But like wise pushing back the GOP lock on those down ballot offices is the only way for any progressive or liberal higher up the ladder to make more than slow incremental improvement.
You can’t compromise when the other side has taken a strict obstructionist approach. You can’t compromise when your opposition have colluded to force you out of the system. More parties aren’t a net good. They’re simply more granular, and potentially ideologically pure. You end up with parties that represent 10, 20, 30, percent of voters rather than 40-50. Not enough to reliably win in isolation, or form functional governments on their own. Which is why you see governments in countries with many political parties form coalitions. The center left party gets 35% of voters and the left left gets 20% so together they’ve got a clear majority. They team up to form a functional, stable-ish government. But things still get weird, problematic and corrupt. You see a lot of situations like conservative or center right parties forming coalitions with multiple small far far right or left wing parties. Tenuous, ideologically divided coalitions that accomplish little, and are prone to collapse. Or parties with overall low support gaining control because while there are more people on the opposite end of the spectrum, those people are split up among many very small and not very influential parties. The smaller, more ideologically extreme or pure parties are often significantly beholden to the larger centrist parties they work with. Alliance with the larger party gives them influence, and their only chance to push their agenda. But they aren’t large enough or strong enough on their own to push those larger parties’ platforms. There’s are reasons you largely see the many party solutions in countries with parliamentary systems of government. And one of the things you see in those parliamentary countries is that when a coalition fails it forces a new election. It doesn’t just stall things out for a while, it actually causes the government to collapse. Some of this of course effects our two party system as well. Our parties have traditionally contained those coalitions within themselves. Until fairly recently both the GOP and DNC have had identifiable conservative, liberal, and centrist wings. The DNC is still a coalition. Largely of a bigger centrist group and a smaller more liberal group. The GOP on the other hand has purged anything but conservatives, while absorbing the most conservative elements from the DNC. Despite this push to ideological purity they haven’t seen a reduction in their share of support from the general public. Despite being (potentially) ideologically out of line with even their base. I think that’s what we’re seeing with Trump. His voters, while mostly hard line republicans, are pretty clearly not all that into some of the deeply embedded conservative ideals the GOP have built their platform around. They are for example not all that interested in things like abortion, libertarian style personal liberty, strict constructionist constitutional interpretations, or all that Jesusy shit that defines the religious right.
That’s a situation that has in the past lead to short lived 3rd parties. Part of one of the large parties splits off into its own unit. In this case you could be looking at Trump leading off a populist, nativist, still fairly extreme party. Which could drive the main body of the GOP to moderate. You could also see a moderate party split off from the GOP leaving it as the party of Trump. Which is what all this rumbling about #nevertrump would point to. These new factions don’t typically last long however. They’re usually absorbed by your main 2 in some fashion in short order, and they realign ideologically after all the mess, lost elections, or failure to prevent whatever they’re trying to prevent. If a moderate splinter faction of the GOP needs to work with the DNC to prevent Trump from Trumpin, on a long enough time line they will likely simply become part of the DNC. If they don’t need to work with the DNC and Trump fails at Trumpin then that splinter faction just becomes the GOP and Trumps insanity fades into the background.