CHICAGO — He walked down a side street, eyes darting here and there, wondering how it would unfold. “What kind of fences will the police have? Will they bring dogs?” Hatem Abudayyeh asked. He stopped in the shadow of the United Center, home of the NBA’s Bulls and the NHL’s Blackhawks and a draw for tens of thousands of pro-Palestinian demonstrators who are expected to protest against U.S. support for Israel at the Democratic National Convention this month. “I hope they don’t militarize it,” he said. “The first statement the police made was about mass arrests. They’ve backed off a...