Warning: Wikipedia contains spoilers

A man standing for election as Mayor of New York City, Stephen Byerley, is suspected by some people to be a robot. If this is true, it will ruin his campaign because of the hysteria generated, and because robots are not allowed to run for office. He never confirms or denies his fleshly status, but while he is campaigning someone rushes the stage and he punches the intruder away. This confirms that he is human in the minds of most people, because it violates the First Law. Susan Calvin is not convinced because a robot can hit another robot.

This is about the public's distrust and fear of robots, despite the fact that a robot is the best candidate for mayor. Many people choose to see Asimov's treatment of technophobia as an allegory to the anti-Semitism he experienced himself.