When activists from the Black Lives Matter movement arrived at a campaign rally for Hillary Rodham Clinton last month with plans to disrupt the event, they were blocked at the door by Secret Service agents and herded into an overflow room. No room, they were told.

A noisy spectacle was averted, but the news spread quickly on social media, and Clinton staffers had to scramble.

Continue reading Candidates interrupted: Why presidential hopefuls are getting heckled by allies →