Vehicles with Trump flags halted traffic Sunday on the Garden State Parkway in New Jersey and jammed the Mario M. Cuomo Bridge between Tarrytown and Nyack, New York. Another pro-Trump convoy in Virginia ended in a tense shouting match with protesters as it approached a statue of Robert E. Lee in Richmond.

In Georgia, a rally for Democrats was canceled shortly before it was scheduled to begin Sunday, with organizers worried about what they feared would be a “large militia presence” drawn by President Donald Trump’s own event nearby.

As the nation races toward Election Day, the tensions and acrimony surrounding an extraordinarily divisive campaign, coming on the heels of a summer of protests and racial unrest, are bleeding into everyday life and adding further uncertainty to an electoral process in which Trump has not committed to a peaceful transfer of power.

Sunday’s incidents came a day after a group of Trump supporters in Texas, driving trucks and waving Trump flags, surrounded and slowed a Biden-Harris campaign bus as it drove on Interstate 35, leading to the cancellation of two planned rallies. The FBI confirmed Sunday that it was investigating the incident.

On Saturday, Trump tweeted a video of the incident with a message, “I love Texas!” After the FBI announced it was investigating, he tweeted again, saying, “In my opinion, these patriots did nothing wrong,” and instead “the FBI & Justice should be investigating the terrorists, anarchists, and agitators of ANTIFA.”

In Graham, North Carolina, a get-out-the vote rally Saturday ended with police using pepper spray on some participants, including young children, and making numerous arrests. Organizers of the rally called it flagrant voter suppression.

“These people are afraid,” the Rev. Gregory B. Drumwright, his eyes still burning, said as he assailed the police action in Graham. “There’s a climate of fear around this.”

And those were just the incidents that were caught on video. Kristen Clarke, executive director of the Lawyers’ Committee for Civil Rights Under Law, a voting rights group, said there had been many more. The group settled a lawsuit last month against officials in Graham who they accused of violating the First Amendment rights of protesters.

“We are very concerned about groups lurking and trying to intimidate voters in particular communities,” Clarke said. Her group’s election protection hotline received calls from nearly a dozen counties in Florida just over the past week, she said, reporting individuals or groups harassing voters at the polls.

“We want voters to know these sporadic incidents are being addressed, and we want them to be able to cast their ballot,” Clarke said.

Law enforcement authorities are increasingly worried, too — not just about what they have already seen, but also about what has been threatened, especially online.

Most of the internet threats have not migrated to the nation’s streets, according to a senior law enforcement official who has reviewed Homeland Security Department bulletins and warnings as well as online activity from instigators on the political right and left. But law enforcement officials fear that online posts by instigators could materialize into violent acts.

Trump supporters mounted a motorcade across the New York City region Sunday, waving flags and cheering for the president while clogging traffic on key arteries.

The supporters were spotted crossing the Mario M. Cuomo Bridge over the Hudson River in the city’s northern suburbs and bringing the busy Garden State Parkway in New Jersey at least partly to a standstill. Officials in New Jersey told a local newspaper that the motorcade stopped near the Cheesequake service area — about 30 miles outside New York City — and “backed traffic up for about 5 miles.”

Supporters waved Trump flags, leaned out of their vehicles wearing Make America Great Again hats and honked and cheered.

The Mario M. Cuomo Bridge might have been a symbolic target for Republicans — it is named for the deceased father of Gov. Andrew Cuomo, a Democrat who has quarreled frequently with Trump.

A separate set of anti-Trump protesters marched in New York City to counter the pro-Trump caravans, leading to some scuffles and arrests.

Groups that monitor voting have been preparing for intimidation at the polls at least since September, when protesters disrupted voters at a polling location in Fairfax, Virginia.

Of particular concern are militia groups like the Proud Boys and Oath Keepers, whose members have lurked on internet chat boards like 4Chan. “We are keeping an eye on them,” said Joanna Lydgate, national director of the Voter Protection Program, which works closely with law enforcement on voting issues.

Law enforcement officers can be a complicating factor in protecting voters. While their presence can be welcome to help calm tensions, they can also create anxieties. Ria Thompson-Washington, an executive vice president with the National Lawyers Guild, said she had been in Georgia since mid-October, when early voting began in the state, and had witnessed “a heavy police presence” at the polls.

All of this has created extraordinary uncertainty, with fears driven not only by the potential outcome of the election but by the tensions that might erupt in the days and weeks after Election Day.

“People are upset, and scared, and frustrated,” said Caitlin Foley, a physician in Philadelphia. “I think there will be unrest, regardless of whichever candidate is in the lead.”

Turmoil has defined 2020. More than 230,000 Americans have died of COVID-19; the economy has cratered, and racial tension has sparked unrest across the country.

Gun stores have seen their stocks depleted as sales have soared. One survey of adults across the country, conducted in October by the National Police Foundation and Elucd, a data research firm, found that some three-quarters of respondents worried that the election would spur civil unrest. Across the political spectrum, there was a sense that the election carried enormous stakes in terms of determining the future of the country.

“I’m encouraged that more than 90 million Americans have already cast their ballots, which, if you do the math, is the equivalent of the entire 1996 presidential election,” Jeh C. Johnson, who served as secretary of Homeland Security during the Obama administration, said Sunday on the CBS program “Face the Nation.” “But we cannot discount the possibility,” he added, “of some trouble or unanticipated events, given the tension that exists out there.”

In an interview on ABC, Jason Miller, an adviser to the Trump campaign, said that Republicans were ready for a legal battle over ballots that have not been counted by Tuesday. He claimed that Democrats expect Trump to be ahead on election night, “and then they’re going to try to steal it back after the election.”

Even prominent Republicans pushed back on the statement, saying that the counting of ballots almost never ends on election night and that any move to end the count that quickly would be an extraordinary breach of democratic practices.

Miller deflected questions about the highway disruptions by Trump supporters, saying he was “more concerned with downtown Washington businesses having to board up their windows in anticipation of lawless, violent Biden supporters rioting and looting on Tuesday night.”

Not all the political activity on Sunday was disruptive.

In Atlanta, from the virtual pulpit of Ebenezer Baptist Church, the storied congregation once led by Martin Luther King Jr., there was a call for calm and a plea for agitators to stay away.

“In the wake of an election, I say to the Proud Boys and to antifa and to other militias and armed groups, Atlanta does not want your foolishness,” the Rev. Robert M. Franklin Jr., a candidate in a runoff election to serve the final month of Rep. John Lewis’ term in Congress, said in a sermon.

In Harrisburg, Pennsylvania, Annie Bravacos, 17, said she had felt a creeping dread about the election, and since she and her friends were too young to vote, they decided to canvass on a rainy Sunday afternoon.

“It’s easy to just get terrified about that, so just doing this, I guess, is what makes us feel better,” she said. “It’s, you know, we’re actually doing something, even if it’s small.”

In Ashland, Kentucky, Mark Carlisle, whose blue pickup flies two American flags and booms out patriotic songs from a speaker, said he was more concerned about ballot tampering than anything happening at his local polling station in a school.

“My ballot getting messed with? Yes. Me afraid to go somewhere? No,” said Carlisle, a 58-year-old building contractor, explaining why he refused to vote by mail or vote early.

In Durham, North Carolina, Garrett Langley Henson was updating his website last week when an unknown number popped up on his phone. When Langley Henson answered, a prerecorded voice told him to “stand back, stay home, stay safe,” and then hung up. He received the same call, but from a different number, the next day.

“The undertone was very menacing,” Langley Henson said.

In Graham, North Carolina, a city of roughly 15,000 people between Greensboro and Durham, police said protest organizers had failed to coordinate with city officials in planning their rally, and that it became “unsafe and unlawful.” Officials disputed any accusations of trying to thwart voters from getting to the polls.

Police said that eight people were arrested on suspicion of resisting the officers and failing to disperse. One was charged with assaulting a law enforcement officer. The department also said officers fired a “mild irritant” on the ground and not directly at protesters.

Drumwright tried to preach a message of resilience Sunday. For generations, obstacles had stood in the way of voting for African Americans. And this, in his view, was the latest iteration.

“We’re still having to march, to protest, to petition, to speak out, to demonstrate, to activate,” Drumwright said. “We are shaken,” he added. “But we are not broken.”