Story highlights Sanders aide Jeff Weaver issues warning

Says Sanders is better candidate to beat Trump

Washington (CNN) Bernie Sanders' campaign manager Jeff Weaver sent a sharply worded fundraising appeal on Wednesday, saying that Democrats "court disaster" by nominating Hillary Clinton.

He also insisted -- despite the fact that Sanders trails Clinton in both pledged delegates and superdelegates and faces a nearly impossible path to the nomination -- that there will be a contested Democratic National Convention.

"The Democratic Party must decide if they want the candidate with the momentum who is best positioned to beat (Donald) Trump or if they are willing to roll the dice and court disaster simply to protect the status quo for the political and financial establishment of this country," Weaver wrote.

He cited a "scary" Quinnipiac University poll of swing states Florida, Ohio and Pennsylvania showing tight races between Clinton and presumptive GOP nominee Donald Trump -- races that Sanders performed slightly better in, though within the poll's margin of error.

"Because we must do everything we can to defeat Trump in November, our mission is to win as many pledged delegates as we can between now and June 14," Weaver wrote. "Then we're going to have a contested convention."

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