Senator Bernard Sanders, an independent from Vermont who calls himself a socialist, was riding in the back seat of a rented blue minivan this week when his aide abruptly announced they were being pulled over by the Iowa State Police for speeding.

“Hi ya, I’m Senator Bernie Sanders, how ya doing?” Mr. Sanders piped up, in his unmistakable Brooklyn accent, after the aide explained to the police officer that they were late for the senator’s appearance here. The officer issued no ticket, just a warning to slow down: “No need making a headline for something silly.”