“It’s people who are in charge keeping their friends in power,” said Tom Carroll, 32, a union plumber who lives in Bethpage, N.Y., summing up how he viewed the electoral system. Mr. Carroll, who was at Mr. Trump’s rally on Long Island on Wednesday, expressed irritation at a system that does not always abide by the one person, one vote concept. “In other countries, we pay to fix their election systems and they get their fingers colored with fingerprint ink when they vote,” he added. “What’s the point of everyone voting if the delegates are going to do what they want?”

Even if superdelegates did not exist, Mr. Sanders would still trail Mrs. Clinton by more than 200 delegates. And his hopes of catching her in the traditional delegate race are looking increasingly thin with several large states favorable to her yet to vote, including New York and Pennsylvania.

His supporters, however, say their votes are effectively being nullified by the superdelegates.

“Our presidents, our congressmen, anyone in Washington, should not be decided by anyone but the public,” said Jordan Float, 25, a nursing assistant at a Philadelphia hospital, and a volunteer with the Sanders campaign.