By Robert Snell From The Detroit News A key participant in the trial of four men accused of plotting to kidnap Michigan Gov. Gretchen Whitmer has tested positive for COVID-19, forcing the judge to halt one of the nation’s most important cases of alleged extremism. Chief U.S. District Judge Robert Jonker postponed the trial in federal court in Grand Rapids until at least Thursday, according to an order filed in federal court on Sunday afternoon. The judge’s order does not identify who tested positive for COVID-19 and instead refers to an “essential trial participant.” “Assuming no other complications, the court hopes to re-convene trial Thursday,” Jonker wrote. The development illustrates the complications of resuming trials during the pandemic. Jonker has followed Centers for Disease Control guidelines, which do not recommend masks in counties, like Kent, with a low risk of transmission, and has not required trial participants to wear masks. …