Bernie Sanders Bernie SandersKenosha will be a good bellwether in 2020 Biden's fiscal program: What is the likely market impact? McConnell accuses Democrats of sowing division by 'downplaying progress' on election security MORE on Monday said the movement he has built while running for president is the future of the Democratic Party.

"If you look at every primary and every caucus, we are winning by very large numbers the votes of those 45 years and younger," he told a crowd in Evansville, Ind.

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"Our ideas, the political revolution transforming America, are the ideas for the future of this country and the future of the Democratic Party.”

Running to the left of front-runner Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE, Sanders has become a progressive champion, winning significant support from younger voters and college students.

Throughout his speech, he highlighted his more liberal stances when compared with Clinton, including on raising the federal minimum wage and hydraulic fracturing. And he accused Republicans of seeking to hold America back from making progress.

While Sanders's positions have energized the party's base, he has only an outside shot of winning the party's nomination.

He trails Clinton by more than 300 pledged delegates, according to The Associated Press. When Clinton's huge lead among party superdelegates is included, she needs to win just 21 percent of the remaining pledged delegates to wrap up the nomination.

Clinton holds a slight lead in polls of Indiana ahead of Tuesday’s primary. A few polls have shown the race as close as 3 or 4 percentage points, but only Sanders chose to hold events in the state the day before the primary. Clinton decided to go to West Virginia instead.

During his rally, the Vermont senator railed against the superdelegate system, which allows about 700 party loyalists to cast their own votes for the party’s nominee on the floor of the Democratic National Convention. Sanders has argued the system unfairly hurts him, noting that he's won about 45 percent of pledged delegates so far but only 7 percent of superdelegates.

"The way the system works is you have establishment candidates who win virtually all of the superdelegates. It makes it hard for insurgent candidacies like ours to win," he said.

Sanders has long argued for open primaries, which allow independents to participate, a call he repeated Monday in light of his success with independent voters.

"I hope the Democrats at the national convention understand that while independents may not be able to vote in certain Democratic primaries, they do vote in the general election," he said.

- This story was updated at 3 p.m.