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.), a potential 2016 presidential contender, slammed the national media’s coverage of 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 on Tuesday, saying the press and public "don't know" where she stands on important issues.

“Why don’t you tell me what Hillary Clinton is campaigning on, do you know?” he said on MSNBC’s “Live with Thomas Roberts,” when asked if he believed her campaign message that she’s running to represent the “little guy."

“You don’t know and I don’t know and the American people don’t know.”

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Sanders mocked the media's fascination with Clinton's early campaign van, which she has nicknamed the "Scooby Doo van."

“I’m sure there is great national interest about the Scooby van, I can’t think of an interest of more significance to the American people,” Sanders said.

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“I would hope very much that serious debate on serious issues is what we do in any campaign,” he added.

Sanders continues to flirt with a presidential bid of his own and has regularly chimed in about the need for a candidate who represents progressive Democrats.

The long-time senator has repeatedly called for significant campaign finance reform and criticized the ability of super-PACs to raise unlimited sums of money.

Sanders didn’t give into questioning on whether Clinton’s decision to enter the race on Sunday would prompt him to do the same.

“We’re going to make that decision pretty soon,” Sanders said.

In her first public remarks of the campaign on Tuesday, shortly after Sanders's appearance, Clinton announced four planks of her campaign, one of which is campaign finance reform.

"We need to fix our dysfunctional political system and get unaccountable money out of it once and for all, even if it takes a constitutional amendment,” she said during an event at Kirkwood Community College in Monticello, Iowa.

Her other proposals include building the “economy of tomorrow,” strengthening both families and communities and protecting the country from present and future threats.