Democratic presidential candidate 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 Sunday said there will be a "contested contest."

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In a news conference from Washington, D.C., on Sunday, the Vermont senator urged superdelegates from states where he has won the majority of the vote to reconsider their support.

"It is virtually impossible for Secretary Clinton to reach the majority of convention delegates by June 14 with pledged delegates alone," he said.

"She will need superdelegates to take her over the top. The convention will be a contested contest," he said.

Sanders said during the news conference he expects to do well in the upcoming primaries. Indiana votes Tuesday, where a new poll shows Sanders trailing Democratic 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 by 4 points.

He said he has won state after state after a strong majority of younger people have voted for him, noting he hopes to win Indiana in next week's primary. His campaign has sparked energy and excitement, he said, which will translate to a large voter turnout in November.

Sanders then detailed the delegate math, saying that to win the majority of pledged delegates, he needs 65 percent of the remaining delegates in the upcoming contests.

"There are 10 states remaining where we are going to be vigorously competing, plus the District of Columbia, Puerto Rico, the Virgin Islands and Guam," he said.

"We believe that we are in a very strong position to win many of these remaining contests and we have an excellent chance to win in California, the state with far and away the most delegates."

He admitted that the road ahead is a "tough road to climb," but not an "impossible road to climb."

"We intend to fight for every vote in front of us and for every delegate remaining," he said.

"In terms of super delegates," he said, "obviously we are taking on virtually the entire Democratic establishment."

He said many of the super delegates committed themselves to his rival Hillary Clinton even before Sanders got into the race.

"While we have won 45 percent of the pledged delegates in real campaigns where the people have spoken … we have won only 7 percent of the superdelegates," he said, contrasting the number of superdelegates he's secured with how many Clinton has.

"Those superdelegates in states where either candidate, Secretary Clinton or myself, has won a landslide victory, those superdelegates ought to seriously reflect on whether they should cast their superdelegate vote in line with the wishes of the people of their states."

He also touted his poll numbers in head-to-head match ups with Republican presidential front-runner Donald Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE, saying superdelegates should look at who would be the best candidate to defeat Trump in a general election.

"Where Secretary Clinton and I strongly agree, and where every delegate to the Democratic Convention strongly agrees is that it would be a disaster for this country if Donald Trump or some other right-wing Republican to become president of the United States," he said.

"Therefore, it is incumbent upon every super delegate to take a hard and objective look at which candidate stands the better chance of defeating Donald Trump and other Republican candidates and in that regard I think the evidence is extremely clear."

"We must have the strongest candidate to defeat Trump or another Republican and I think the objective evidence is that I am that candidate."

— This post was updated at 3:21 p.m.