Throwing a sandwich at a federal agent turned Sean Charles Dunn into a symbol of resistance against President Donald Trump’s law-enforcement surge in the nation’s capital. This week, federal prosecutors are trying to persuade a jury of fellow Washington, D.C., residents that Dunn simply broke the law. Securing a trial conviction could prove to be equally challenging for Justice Department prosecutors in Washington, where murals glorifying Dunn's sandwich toss popped up virtually overnight.