GRAND RAPIDS, Mich. — It was one of the country’s highest-profile domestic terrorism cases: An alleged plot to kidnap Gov. Gretchen Whitmer of Michigan, eliminate her security detail and perhaps touch off a civil war. But after a trial in which prosecutors portrayed the four defendants as threats to democracy, jurors on Friday acquitted two of the men and said they were unable to reach verdicts for the two others.

The result was a major blow to the Justice Department, which during the Biden administration has made domestic terrorism one of its top priorities in the aftermath of the Jan. 6, 2021, riot at the U.S. Capitol.

The defendants in the Michigan trial were arrested weeks before the 2020 election, and the case was seen by some as revealing increasingly combative discourse among certain right-wing groups. But a series of missteps during the investigation, and the eventual failure to win any convictions against the men who went to trial, raises questions about the ability of federal law enforcement, when it infiltrates right-wing groups, to develop convincing cases without infringing on the rights to speak freely and own weapons.

Prosecutors built their case on a trove of audio recordings and encrypted texts from 2020 in which some of the men vented about Covid-19 restrictions, spoke about political violence and debated the best way to kidnap Ms. Whitmer, a Democrat, from her vacation home in northern Michigan.

Yet the very existence of those recordings and text conversations underscored defense lawyers’ theory of the case: that the supposed plot had been conceived and nudged ahead by a network of F.B.I. agents and informants who preyed on the worst instincts of their loose-lipped targets. The defense lawyers described the men on trial as big talkers who were never going to commit any kidnapping.

“Words hurt you? Words scare you?” Daniel Harris, who was acquitted of all the charges against him, had said when he took the stand in his own defense. Mr. Harris insisted that he never joined any plot, and he referred derisively to an F.B.I. informant, Dan Chappel, who had testified earlier in the trial that he feared the group’s antigovernment and anti-law-enforcement rhetoric would escalate into violence.

Issues with the actions of some F.B.I. agents also loomed over the trial, though little of that was discussed explicitly in front of jurors. One F.B.I. agent was fired last year after being charged with domestic violence. Another agent, who supervised Mr. Chappel, tried to build a private security consulting firm based in part on some of his work for the F.B.I., according to a BuzzFeed News report.

“The jury, even though they didn’t get all of it, they smelled enough of it,” said Michael Hills, a lawyer for Brandon Caserta, who was acquitted of the only count against him.

A spokeswoman for the F.B.I.’s Detroit office declined to comment.

The jury of six men and six women, which deliberated for nearly a week, did not reach any verdict on the charges against two defendants, Barry Croft and Adam Fox, whom prosecutors portrayed as having a leadership role. A judge declared a mistrial for those men and ordered them held in jail.

Others have also been charged in connection with the investigation. Two men, Ty Garbin and Kaleb Franks, pleaded guilty before the trial to kidnapping conspiracy and testified against the defendants in the federal case. Eight other men were charged with related crimes in state court.

Outside the courthouse, Andrew Birge, the top federal prosecutor in western Michigan, did not respond when asked directly whether his office would seek a second trial for Mr. Croft and Mr. Fox. But he said in a statement that he was limited in what he could say because “two defendants now await re-trial.”

“Obviously we’re disappointed in the outcome,” Mr. Birge said. He added: “We still believe in the jury system, and really, there’s not too much more I can say at this time. I appreciate the time the jury put in. They listened to a lot of evidence, deliberated quite a bit.”

During weeks of testimony at the federal courthouse in Grand Rapids, prosecutors showed jurors inflammatory social media posts and chat messages from the defendants, and presented audio secretly recorded by Mr. Chappel and other informants. One former co-defendant who pleaded guilty testified that he hoped to set off a chain of events that would prevent Joseph R. Biden Jr. from being elected president and would perhaps foment a civil war.

“That was the whole plan: They wanted to kick that off by kidnapping the governor,” Nils Kessler, a federal prosecutor, said during closing arguments.

But the prosecution’s case was hampered by a lack of clarity on what exactly the men were accused of plotting. No attack ever took place and no final date for an abduction was set, testimony showed. The details of the alleged plan sometimes differed drastically from prosecution witness to prosecution witness.

The F.B.I. informant, Mr. Chappel, said he believed that the group planned to kill Ms. Whitmer, whose handling of the Covid-19 pandemic had infuriated the men. Mr. Garbin, who earlier pleaded guilty in the case, said he thought the group of men might abandon the governor in a boat in the middle of Lake Michigan. Mr. Franks, who also pleaded guilty, told jurors that he had hoped to die in a shootout with the governor’s security detail.

“There was no plan to kidnap the governor, and there was no agreement between these four men,” Joshua Blanchard, a lawyer for Mr. Croft, said in closing arguments. He said the government tried to conjure up a conspiracy by using a network of informants and undercover agents, and that “without a plan, the snitches needed to make it look like” there was movement toward a plan.

As the pandemic began in 2020, Ms. Whitmer, a first-term governor with a national profile, took a more restrictive approach than some other Midwestern leaders, keeping many rules in place even when new virus case numbers dropped. At the time of the arrests of the men, in October 2020, the governor criticized President Donald J. Trump’s rhetoric about hate groups.

After the verdicts were announced, Ms. Whitmer’s chief of staff issued a statement that called for “accountability and consequences for those who commit heinous crimes,” adding that “without accountability, extremists will be emboldened.”

In a separate statement, Lt. Gov. Garlin Gilchrist, a Democrat, called the verdict disappointing. “Our differences must be settled at the ballot box, not through violence,” he said. “We need to be honest and clear about what causes violence by extremists and do all we can to address the root cause of it.”

Defense lawyers sought to portray Mr. Chappel, a military veteran who pretended to befriend the men while surreptitiously recording them for the government, as a leader of the group. They noted that Mr. Chappel, known as “Big Dan,” sometimes led training outings and gave advice about the plot, including when he floated the idea of using explosives outside the governor’s house when she was not there. On one training outing, Mr. Chappel and others videotaped themselves jumping out of Mr. Franks’s bright-blue PT Cruiser and taking cover behind its doors while they fired rifles.

Legal observers questioned after the verdict whether the F.B.I. might have moved in too early to make the arrests, before the men tried to carry out any abduction or even set a date for an attack. On the day of the arrest, testimony showed, some of the defendants thought they were going to get free gear from an undercover F.B.I. agent before lunch at Buffalo Wild Wings. Instead, a phalanx of F.B.I. agents took them into custody.

“I think the message that it shows to law enforcement is, before you arrest somebody and bring the charges, you’d better be darned sure that you’ve got a locked, tight case,” said Matthew Schneider, who served as the top federal prosecutor in eastern Michigan during Mr. Trump’s presidency, and who said he was involved in the early stages of the investigation. “Did they have to arrest them at that time? Could they have waited?”

R. Michael Bullotta, a defense lawyer who previously worked as an assistant U.S. attorney in Detroit, said that he, too, wondered whether the arrests were premature. Mr. Bullotta also said that the sheer quantity of informants might have hampered the case.

“I don’t know that they needed to have as many informants as they had,” Mr. Bullotta said. “That almost made it look like it was a government party as opposed to just having one informant reporting to the F.B.I.”

As some of the defense lawyers acknowledged in court, many of the men were recorded making offensive remarks, or statements advocating violence, about law enforcement officers, Ms. Whitmer or politicians in general. One F.B.I. agent testified that Mr. Caserta had posted on social media that the Second Amendment gave people the right to “kill agents of the government when they become tyrannical.”

The chief tension of the case was whether speech like that crossed a line into criminal activity.

“If I don’t like the governor and it’s rough talk, I can do that in our country,” Mr. Hills said after the verdict was announced and his client left the courthouse.

Glenn Thrush contributed reporting.

[Read More…]