This article seems relevant:
Where the System May Break
If the link to that article is paywalled, Vox has similar coverage of the same "war game".
How to avert a post-election nightmare
From that article:
Essentially, mess with the electoral college. I can see that happening. A state with a GOP governor goes narrowly Democratic? - then Governor declares all mail-in votes suspect and invalidates them. Orders election workers to look more closely for spoiled ballots - starting in Dem districts. Its not about creating fake votes, that's too hard. But it is easy to throw away valid votes.
There have even been scenarios proposed where a single state sends two conflicting delegations to the EC - one from a governor, one from the legislature. And the legal remedies to that are not all that clear cut.
I keep thinking of Texas. Many Republicans love Texas, they imagine a state filled with well-armed big men named "Hoss" and "Bubba", who drive big trucks. They feel that Texas is pure GOP territory, I think they can't imagine Texas voting Dem - but it could happen. (Personally, I don't think it will, not yet, but for the sake of argument we'll imagine it does as some models suggest is possible.) One could imagine the state GOP machine kicking into overdrive to ensure that the EC from Texas stays Republican - it has to. It is their state, their
Republican state, no election can change that. So they mess with the EC somehow.
If it goes to the Supreme Court, expect the
lame duck Senate to try to impeach RBG by claiming she is no longer mentally competent. Regardless of how the election goes, Mitch McConnell will still be the Senate Majority leader until inauguration day. I he thinks he needs to get rid of Dem SC Justice, he'll try, he's shown himself to be partisan to the point of immorality.
Remember that if anything happens, it will all be couched in very legalistic terminology. It won't be Trump crying and whining and throwing a tantrum. It will be lawyers citing laws, citing the constitution as reasons for throwing away votes, for sending EC delegations that don't match a given state's popular vote. Lots of legal cites of state laws and constitutions are they relate to appointing EC delegates and determining how those delegates vote.
If things go really, really south (which I don't actually expect), then one would expect Trump (or Pence) to cite this or that portion of the Constitution as the justification for suspending certain other parts of the Constitution and inconvenient laws. Look at most third-world coups, that's how they often do it, citing the legal national charter as the justification for suspending that charter. For example, they could make claims about threats to the Second Amendment as justification for this or that - enough rabid militia and Qanon gun nuts would accept any justification if it is coached as a defense of the 2nd.
Don't expect the military to do squat. They'll mostly sit it out, a surprising number of civil wars feature a national military watching from the sidelines until things are more advanced. Some military people may take action, but the big assets will just sit and watch.
I mostly don't think any of that will actually happen - but I would be much happier if I felt more certain of that. Things are pretty bad. We'll have a nice clear winner and peaceful inauguration of the winner. I think.