The mayor of Kansas City, Mo., was turned away from a polling place when he tried to vote in the state’s primary on Tuesday, a development he found frustrating and emblematic of broader problems with the American voting system.

The mayor, Quinton Lucas, said on Twitter that he had been told he “wasn’t in the system” at a polling place he had used for more than a decade. The episode unfolded shortly after he made a video in which he discussed the importance of voting and encouraged people to show up at the polls.