The bus is always the center of attention. Partly because it's a hulking 1970s tour bus that somehow made it from Arizona all the way to Charlotte, but mostly because of what's inscribed on the side of it in thick, black letters. "Sin Papeles, Sin Miedo," it reads in Spanish. "No papers, no fear." Carrying a bunch of undocumented activists, the bus rolled through the country, through states like Arizona, Texas, Louisiana and Georgia, and into Charlotte on the eve of the Democratic National Convention. The activists participated in a march that snaked through Charlotte on Sunday and by Monday,...