WASHINGTON — In October, President Trump declares a state of emergency in major cities in battleground states, like Milwaukee and Detroit, banning polling places from opening.
A week before the election, Attorney General William P. Barr announces a criminal investigation into the Democratic presidential nominee, Joseph R. Biden Jr.
After Mr. Biden wins a narrow Electoral College victory, Mr. Trump refuses to accept the results, won’t leave the White House and declines to allow the Biden transition team customary access to agencies before the Jan. 20 inauguration.
Far-fetched conspiracy theories? Not to a group of worst-case scenario planners — mostly Democrats, but some anti-Trump Republicans as well — who have been gaming out various doomsday options for the 2020 presidential election. Outraged by Mr. Trump and fearful that he might try to disrupt the campaign before, during and after Election Day, they are engaged in a process that began in the realm of science fiction but has nudged closer to reality as Mr. Trump and his administration abandon longstanding political norms.
The anxiety has intensified in recent weeks as the president continues to attack the integrity of mail voting and insinuate that the election system is rigged, while his Republican allies ramp up efforts to control who can vote and how. Just last week, Mr. Trump threatened to withhold funding from states that defy his wishes on expanding mail voting, while also amplifying unfounded claims of voter fraud in battleground states.
“In the eight to 10 months I’ve been yapping at people about this stuff, the reactions have gone from, ‘Don’t be silly, that won’t happen,’ to an increasing sense of, ‘You know, that could happen,’” said Rosa Brooks, a Georgetown University law professor. Earlier this year, Ms. Brooks convened an informal group of Democrats and never-Trump Republicans to brainstorm about ways the Trump administration could disrupt the election and to think about ways to prevent it.
But the anxiety is hardly limited to outside groups.
Marc Elias, a Washington lawyer who leads the Democratic National Committee’s legal efforts to fight voter suppression measures, said not a day goes by when he doesn’t field a question from senior Democratic officials about whether Mr. Trump could postpone or cancel the election. Prodded by allies to explain why not, Mr. Elias wrote a column on the subject in late March for his website — and it drew more traffic than anything he’d ever published.
But changing the date of the election is not what worries Mr. Elias. The bigger threat in his mind is the possibility that the Trump administration could act in October to make it harder for people to vote in urban centers in battleground states — possibilities, he said, that include declaring a state of emergency, deploying the National Guard or forbidding gatherings of more than 10 people.
Such events could serve to depress or discourage turnout in pockets of the country that reliably vote for Democrats.
“That to me is the frame from which all doomsday scenarios then go,” he said.
To ward off such a scenario, Mr. Elias is engaged in multiple lawsuits aimed at making it easier to cast absentee ballots by mail and making in-person voting more available, either on Election Day or in the preceding weeks.
“Since 2016, Donald Trump has shown that he is always ready to sacrifice our basic democratic norms for his personal and political interests,” said Bob Bauer, a Biden senior adviser who is a lawyer for the campaign. “We assume he may well resort to any kind of trick, ploy or scheme he can in order to hold onto his presidency. We have built a strong program to plan for and address every possibility to ensure that he does not succeed.”
Mr. Trump’s campaign derided the anxiety over the election as irrational hand-wringing driven by Democrats’ inability to accept his victory four years ago.
“Hillary Clinton, Stacey Abrams and the entire Democratic Party refused to accept the results of their elections and pushed the Russia collusion conspiracy theory for years,” said Tim Murtaugh, the communications director for Mr. Trump’s re-election campaign. “Now Joe Biden’s allies have formed actual conspiracy committees where they’ll work up new hoaxes to further undermine our democracy. They are wasting their time. As President Trump has repeatedly said, the election will happen on Nov. 3.”
The president attacked mail balloting again Sunday morning, with a baseless claim that it would lead to “the greatest Rigged Election in history.” And the Republican National Committee said on Sunday that it and other G.O.P. groups had sued to stop Gov. Gavin Newsom of California from mailing absentee ballots to all of the state’s voters.
Some Democrats have been cautious about voicing their warnings about potential electoral calamities too loudly, for fear that even the suggestion of a tainted election would depress turnout.
“You don’t want to set up a perception based on the theory that elections don’t matter,” said Ari Rabin-Havt, who was a deputy campaign manager for Senator Bernie Sanders. “You don’t want to tell supporters that nothing you do matters because this guy is going to screw it up.”
Ms. Brooks’s group at Georgetown is not the only one forecasting doomsday scenarios for the election. Ian Bassin, the executive director of Protect Democracy, a nonprofit group dedicated to resisting authoritarian government, last year convened the National Task Force on Election Crises, a bipartisan 51-member group that includes Republicans such as Michael Chertoff, the former homeland security secretary. The group is dedicated to envisioning and presenting plans for scenarios that could wreck the 2020 presidential election.
The task force began with 65 possibilities before narrowing the list early this year to eight potential calamities, including natural disasters, a successful foreign hack of voting machines, a major candidate’s challenging the election and seeking to delegitimize the results, and a president who refuses to participate in a peaceful transfer of power.
Among the scenarios they eliminated when making final cuts in January, ironically, was a killer pandemic that ravaged the country and kept people homebound before Election Day. After the coronavirus struck, the group reconstituted to publish pandemic-related recommendations for state governments to follow.
The group also produced a 200-page document, which has not been made public. Several members said they had worked on specific scenarios but had not seen the complete draft. They said that while many of the possibilities envisioned an incumbent president’s using the forces of government to his advantage, the report’s authors had been careful not to make the document explicitly about Mr. Trump.
“We hope there are safeguards in place,” said Norman J. Ornstein, a scholar at the American Enterprise Institute who participated in the task force. “Let’s face it, those safeguards ought to include the Senate of the United States and the Justice Department. There’s reason to be nervous.”
Edward B. Foley, a law professor at Ohio State University who participated in the task force, said the 2020 election could resemble the contest of 1876, which nearly split the country a decade after the Civil War.
That election was not decided until Gov. Samuel J. Tilden of New York conceded to Gov. Rutherford B. Hayes of Ohio two days before the inauguration. The outgoing president, Ulysses S. Grant, had made contingency plans for martial law because he was concerned there would be simultaneous competing inaugurations.
“We’re setting ourselves up for an election where neither side can concede defeat,” Professor Foley said. “That suggests that the desire to dispute the outcome is going to be higher than ever.”