Another prosecution witness who also pleaded guilty to the kidnapping conspiracy, Kaleb Franks, testified on Thursday that he also intended to kidnap the governor and had not been forced into the plot by the F.BI. Mr. Franks, who has not yet been sentenced, said he had hoped to die during the attack on the governor. Mr. Franks, 27, said he had been in despair after the deaths of three close family members.

Prosecutors said in the months before the arrests, the men, many of whom were militia members, attended meetings and what they described as “field training exercises” to practice shooting and first-aid. In one exercise, they videotaped themselves jumping out of Mr. Franks’s bright-blue PT Cruiser and taking cover behind its doors while they fired rifles.

Secretly recorded audio and private messages also showed members of the group repeatedly airing grievances about the government, especially about Covid-19 restrictions, and expressing openness to a range of possible attacks. But there has been vast disagreement in court about how close they were to carrying out any attack, and about what their exact plan even was.

Dan Chappel, a military veteran who signed on as an F.B.I. informant in early 2020 after becoming worried about the goals of one militia, the Wolverine Watchmen, pretended to befriend the men who were charged and recorded their interactions for months. As the group began to develop a plan, some of the defendants mused about storming the State Capitol in Lansing or taking Ms. Whitmer in a boat across Lake Michigan or blowing up a bridge to make it harder for police to respond to the kidnapping.

But defense lawyers, who are pursuing an entrapment defense, questioned Mr. Chappel’s role in the plot, pointing out that he helped lead militia training and made suggestions about attack plans. The implication was that, if not for Mr. Chappel, who was receiving instructions from the F.B.I., the plan to kidnap Ms. Whitmer would probably not have moved forward.

Mr. Chappel, who spent parts of several days on the witness stand, said he believed the men intended to kidnap Ms. Whitmer, kill members of her security detail and eventually kill the governor herself after staging a fake trial. But the exact plans for the kidnapping, a date for which had not seen set, seemed to have still been in flux at the time of the arrests, a fact that defense lawyers have seized on.

Mr. Garbin, who had expressed hope of setting off a civil war, testified that he thought they would kidnap Ms. Whitmer, take her out on Lake Michigan, strand her in a boat, drop the motor and leave her there alone. Under cross-examination, Mr. Garbin conceded that no boat had been selected for that mission, and that he did not know how the kidnappers planned to get themselves back to shore.