Nicole Gaudiano

USA TODAY

WASHINGTON -- Fresh off three decisive caucus victories, campaign officials for Sen. Bernie Sanders said Monday he has the momentum to top Hillary Clinton in pledged delegates by June and can win over enough unpledged "superdelegates" to claim the Democratic presidential nomination.

“Reports of our death are greatly exaggerated,” said Jeff Weaver, Sanders’ campaign manager. “We are on a path to victory.”

Clinton still enjoys a nearly insurmountable lead in delegates, but Sanders is pushing back against the notion that she has the nomination virtually locked up.

His campaign on Monday cast Clinton as a “weakened frontrunner” struggling to inspire young voters and draw interest from independents, who could play a crucial role in the general election. Sanders' campaign officials highlighted polls showing he outperforms Clinton in general election matchups against Republican frontrunner Donald Trump.

“This isn’t a blip in the data,” Sanders’ pollster Ben Tulchin said during a conference call with reporters. “This is an overwhelming preponderance of evidence that Bernie is a stronger general election candidate than Hillary Clinton and these are things that Democratic voters in the states ahead and superdelegates, quite frankly, have to consider very seriously.”

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The Clinton campaign, in a later conference call with reporters, was quick to dismiss such optimism.

Sanders' campaign did not say exactly when it expects Sanders to overtake Clinton in pledged delegates. Clinton's lead among those delegates is 1,243 to 975 -- a difference of 268. She also leads Sanders 469 to 29 in superdelegates, the party leaders and elected officials who may support the candidate of their choice at the Democratic convention in July. That brings Clinton’s overall lead to 1,712 to 1,004.

Sanders must win 57% of the remaining pledged delegates to claim a majority of those delegates. That's highly unlikely, especially since he still must face Clinton in states with diverse populations where the former secretary of State typically outperforms him, said Joel Benenson, Clinton’s chief strategist. Clinton is expected to do well, for example, in Pennsylvania, California and especially New York, which she represented in the Senate.

Benenson predicted that Clinton will effectively lock up the nomination on April 26, when Pennsylvania and other eastern states vote.

“We expect to come out of that day with a pledged and total delegate lead that will make clear who the nominee will be, and it’s going to be Hillary Clinton,” he said.

Sanders has pulled in nearly $4 million in contributions since his overwhelming wins on Saturday in Washington State, Alaska and Hawaii. That gives the campaign the resources it needs to compete in the next major contest, Wisconsin on April 5. Sanders will spend Tuesday and Wednesday in the state.

Tad Devine, senior adviser on Sanders' campaign, said neither Sanders nor Clinton will win the nomination based on pledged delegates alone and that superdelegates are key for both candidates.

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Weaver said the campaign’s primary focus is capturing pledged delegates in Wisconsin and in New York on April 19. But the campaign has stayed in communication with superdelegates and has identified a “substantial” number who support Sanders, even though they aren’t prepared to say so publicly, he said.

“It would be easy for them at this point to be pledged to Hillary Clinton, given some of the media narrative and the establishment support she has,” Weaver told reporters. “The fact that they have yet to do that, I think, demonstrates that there is certainly a large number of superdelegates who have some reluctance about Secretary Clinton’s campaign.”

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