Sen. Tim Kaine Timothy (Tim) Michael KaineBarrett seen as a front-runner for Trump Supreme Court pick Biden promises Democratic senators help in battleground states Second GOP senator to quarantine after exposure to coronavirus MORE (D-Va.), the 2016 Democratic vice presidential nominee, is siding with Sen. Bernie Sanders Bernie SandersNYT editorial board remembers Ginsburg: She 'will forever have two legacies' Two GOP governors urge Republicans to hold off on Supreme Court nominee Sanders knocks McConnell: He's going against Ginsburg's 'dying wishes' MORE (I-Vt.) in advocating for the Democratic National Committee (DNC) to end the use of superdelegates, saying that they have "undue influence" over the primary process.

Kaine, who was Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE's running mate last year, sent a letter to the DNC Chairman Tom Perez Thomas Edward PerezClinton’s top five vice presidential picks Government social programs: Triumph of hope over evidence Labor’s 'wasteful spending and mismanagement” at Workers’ Comp MORE on Wednesday pushing the party to no longer use the powerful, unelected delegates, who overwhelmingly sided with Clinton against primary rival Sanders.

"I have long believed there should be no superdelegates. These positions are given undue influence in the popular nominating contest and make the process less democratic,” Kaine wrote in the letter, obtained first by Politico.

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Superdelegates consist of powerful Democratic operatives and elected officials whose votes carry more weight than regularly elected delegates, sometimes trumping the winner of state primary votes.

Sanders received 359 fewer delegates than Clinton in the Democratic primary, yet Clinton won the nomination with 602 superdelegates while Sanders took only 48.

The Vermont senator has been a vocal advocate of abolishing the rule, claiming that Clinton, an establishment candidate, won unfair support from longtime party operatives.

Kaine, a former DNC chairman and superdelegate himself, urged the Unity Reform Commission, a group reviewing and recommending changes to the system, to do away with superdelegates altogether and said he would protest the rule by voting strictly in accordance with his home district in the future.