Sanders fires back at Trump: 'Never tweet'
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Sen. Bernie SandersBernie SandersOvernight Health Care — Presented by National Taxpayers Union — House Dems change drug pricing bill to address progressive concerns | Top Republican rejects Dem proposal on surprise medical bills | Vaping group launches Fox News ad blitz Democrats have reason to worry after the last presidential debate Krystal Ball on Sanders debate performance: 'He absolutely hit it out of the park' MORE (I-Vt.) fired back at Donald TrumpDonald John TrumpGOP congressman slams Trump over report that U.S. bombed former anti-ISIS coalition headquarters US to restore 'targeted assistance' to Central American countries after migration deal Trump says lawmakers should censure Schiff MORE after the brash GOP presidential nominee said Sanders "sold out" and abandoned his supporters.  

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"Never tweet," Sanders posted on Twitter Monday night, just minutes after he ended his speech at the Democratic National Convention, during which he warned that having Trump in the White House would threaten the progressive policies that drove his campaign against presumptive Democratic presidential nominee Hillary ClintonHillary Diane Rodham ClintonGOP warns Graham letter to Pelosi on impeachment could 'backfire' Hillary Clinton praises former administration officials who testified before House as 'gutsy women' Third-quarter fundraising sets Sanders, Warren, Buttigieg apart MORE.
 
Trump has knocked Sanders since he endorsed Clinton. He took aim at the Vermont senator while he was speaking in Philadelphia, saying he "totally sold out to Crooked Hillary Clinton." 
 
"All of that work, energy and money, and nothing to show for it! Waste of time," he added. 
 
Trump has tried to play up frustration among progressive voters as Democrats try to project unity at their four-day event. He also said Monday that former Sanders backers were welcome to join his campaign.