Sanders' campaign manager Jeff Weaver made that case again today in an email to supporters, saying if the Democrats nominated Clinton it would be a 'disaster.'
Weaver pointed to three early polls out of three swing states – Pennsylvania, Ohio and Florida – that showed Trump to be competitive.
'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 said.
'Then we're going to have a contested convention where the Democratic Party must decide if they want the candidate with the momentum who is best positioned to beat 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.'
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