I have no comment on Swammerdami's probability estimates, since I have no clue as to how they were obtained.
Welcome To The ‘Turbulent Twenties’ - NOEMA - September 10, 2020 - Jack A. Goldstone and Peter Turchin
noting
A bipartisan group secretly gathered to game out a contested Trump-Biden election. It wasn’t pretty - The Boston Globe
“All of our scenarios ended in both street-level violence and political impasse,” said Rosa Brooks, a Georgetown law professor and former Defense Department official who co-organized the group known as the Transition Integrity Project. She described what they found in bleak terms: “The law is essentially ... it’s almost helpless against a president who’s willing to ignore it.”
Especially someone who never seems to run out of money for litigation when challenged on his misdeeds.
Using a role-playing game that is a fixture of military and national security planning, the group envisioned a dark 11 weeks between Election Day and Inauguration Day, one in which Trump and his Republican allies used every apparatus of government — the Postal Service, state lawmakers, the Justice Department, federal agents, and the military — to hold onto power, and Democrats took to the courts and the streets to try to stop it.
The Trump Admin didn't quite go that far, however. It was content with filing 62 lawsuits -
Post-election lawsuits related to the 2020 U.S. presidential election - despite losing almost all of them. But then came the counting of the electoral votes on January 6, 2021, and Donald Trump invited his followers to attack the US Capitol. It was a very unexpected sort of move.
They warn:
A close election this fall is likely to be contested, and there are few guardrails to stop a constitutional crisis, particularly if Trump flexes the considerable tools at his disposal to give himself an advantage.
Tools that are now in the Biden Admin's hands, but Joe Biden is a firm institutionalist.
“He doesn’t have to win the election,” said Nils Gilman, a historian who leads research at a think tank called the Berggruen Institute and was an organizer of the exercise. “He just has to create a plausible narrative that he didn’t lose.”
So he did, with his Big Lie. Then about Donald Trump calling mail-in ballots an enabler of election fraud. When asked if he will accept the election results, he told Chris Wallace of Fox News “I’ll have to see.”
To some participants, the game was a stark reminder of the power of incumbency. “The more demonstrations there were, the more demands for recounts, the more legal challenges there were, the more funerals for democracy were held, the more Trump came across as the candidate of stability,” said Edward Luce, the US editor of the Financial Times, who played the role of a mainstream media reporter during one of the simulations. “Possession is nine-tenths of the law.”
This time, it's Joe Biden who's the incumbent.
In multiple scenarios, officials on both sides homed in on narrowly decided swing states with divided governments, such Wisconsin, Michigan, and North Carolina, hoping to persuade officials there to essentially send two different results to Congress. If a state’s election is disputed, a legislature controlled by one party and governor of another each could send competing slates of electors backing their party’s candidate.
That didn't happen, but Trump's campaigners tried to recruit some slates of fake electors.
Both sides turned out massive street protests that Trump sought to control — in one scenario he invoked the Insurrection Act, which allows the president to use military forces to quell unrest. The scenario that began with a narrow Biden win ended with Trump refusing to leave the White House, burning government documents, and having to be escorted out by the Secret Service. (The team playing Biden in that scenario, meanwhile, sought to patch things up with Republicans by appointing moderate Republican governors, including Charlie Baker of Massachusetts, to Cabinet positions.)
Trump didn't go this far, however.
As to the Jan. 6 attacks, I recall that some anti-Trump activists decided to stay home because they didn't want a fight with the Trumpies that Trump invited to DC on that day. They didn't want some pretext for a police / National-Guard crackdown, even if they were the ones attacked.
The scenario that produced the most contentious dynamics, however, was the one in which Trump won the Electoral College — and thus, the election — but Biden won the popular vote by 5 percentage points. Biden’s team retracted his Election Night concession, fueled by Democrats angry at losing yet another election despite capturing the popular vote, as happened in 2000 and 2016. In the mock election, Trump sought to divide Democrats — at one point giving an interview to The Intercept, a left-leaning news outlet, saying Senator Bernie Sanders would have won if Democrats had nominated him. Meanwhile, Biden’s team sought to encourage large Western states to secede unless pro-Democracy reforms were made.