The trial Mr. Dunn faced in Washington was the product of a monthslong effort to exact some — or any — penalty against him, after the Trump administration tried and failed to secure a felony indictment against Mr. Dunn in August. Online and in local culture, the Subway-brand sandwich and Mr. Dunn’s chucking of it, which was captured on video that went viral, have became symbols of resistance to President Trump’s militarized law enforcement sweeps in Washington that have regularly recurred since August.