A Texas jury will soon decide whether a convoy of supporters of then-President Trump violently intimidated former Democratic lawmaker Wendy Davis and two others on a Biden-Harris campaign bus when a so-called “Trump Train” boxed them in for more than an hour on a Texas highway days before the 2020 election.

The trial, which began on September 9, resumes Monday and is expected to last another week.

Attorneys for the plaintiffs argued that six of the Trump Train drivers violated state and federal law. Lawyers for the defendants said they did not conspire against the Democrats on the bus and that their actions are protected speech.

Dozens of cars and trucks organized by a local Trump Train group swarmed the bus on its way from San Antonio to Austin on October 30, 2020. It was the last day of early voting in Texas for the 2020 general election, and the bus was scheduled to make a stop in San Marcos for an event at Texas State University.

Video recorded by Ms. Davis shows pickup trucks with large Trump flags aggressively slowing down and boxing in the bus as it tried to move away from the Trump Train. One defendant hit a campaign volunteer’s car while the trucks occupied all lanes of traffic, slowing the bus and everyone around it to a 15 mph crawl.

Those on the bus — including Ms. Davis, a campaign staffer and the driver — repeatedly called 911 asking for help and a police escort through San Marcos, but when no law enforcement arrived, the campaign canceled the event and pushed forward to Austin.

San Marcos settled a separate lawsuit filed by the same three Democrats against the police, agreeing to pay $175,000 and mandate political violence training for law enforcement.

Ms. Davis testified that she felt she was being “taken hostage” and has sought treatment for anxiety. In the days leading up to the event, Democrats were also intimidated, harassed and received death threats, the lawsuit said.

“I feel like they were enjoying making us afraid,” Ms. Davis testified. “It’s traumatic for all of us to revisit that day.”

In opening statements, an attorney for the plaintiffs said convoy organizers targeted the bus in a calculated attack to intimidate the Democrats in violation of the “Ku Klux Klan Act,” an 1871 federal law that bans political violence and intimidation.

“We’re here because of actions that put people’s lives in danger,” said Samuel Hall, an attorney with the law firm Willkie Farr & Gallagher. The plaintiffs, he said, were “literally driven out of town by a swarm of trucks.”

The six Trump Train drivers succeeded in making the campaign cancel its remaining events in Texas in a war they believed was “between good and evil,” Mr. Hall said.

Two nonprofit advocacy groups, Texas Civil Rights Project and Protect Democracy, also are representing the three plaintiffs.

Attorneys for the defendants, who are accused of driving and organizing the convoy, said they did not conspire to swarm the Democrats on the bus, which could have exited the highway at any point.

“This was a political rally. This was not some conspiracy to intimidate people,” said attorney Jason Greaves, who is representing two of the drivers.

The defense also argued that their clients’ actions were protected speech and that the trial is a concerted effort to “drain conservatives of their money,” according to Francisco Canseco, a lawyer for three of the defendants.

“It was a rah-rah group that sought to support and advocate for a candidate of their choice in a very loud way,” Mr. Canseco said during opening statements.

The defense lost a bid last month to have the case ruled in their favor without a trial. The judge wrote that “assaulting, intimidating, or imminently threatening others with force is not protected expression.”