CHICAGO — Two years after the gruesome presidential primary of 2016 left Democrats bitterly divided, the Democratic National Committee adopted major reforms Saturday to reduce the outsized influence of unpledged delegates, known as superdelegates.

In a majority vote, the DNC passed a measure to block superdelegates — elected officials and party leaders — from casting a vote for any presidential candidate unless a second ballot is required at the 2020 national convention, stripping them of power. The change comes after supporters of Sen. Bernie Sanders, I-Vt., asserted superdelegates gave Hillary Clinton an unfair advantage, creating a perception that she had the nomination sewn up before the primary.