Sanders, Trump in Twitter fight over Clinton endorsement
© Getty Images

Shortly after throwing his support behind his former primary rival on Tuesday, Sen. Bernie SandersBernie SandersSanders to join teachers, auto workers striking in Midwest Krystal Ball tears into 'Never Trump' Republicans 2020 Democrats defend climate priorities in MSNBC forum MORE took to Twitter to mock presumptive GOP nominee Donald TrumpDonald John TrumpJulián Castro: It's time for House Democrats to 'do something' about Trump Warren: Congress is 'complicit' with Trump 'by failing to act' Sanders to join teachers, auto workers striking in Midwest MORE for criticizing the endorsement. 

"Big talk from the same guy who was too afraid to debate Bernie in California," said a tweet on Sanders's campaign account, responding to a message from Trump that said Sanders had "totally sold out to Crooked Hillary ClintonHillary Diane Rodham ClintonMissing piece to the Ukraine puzzle: State Department's overture to Rudy Giuliani On The Money: Trump downplays urgency of China trade talks | Chinese negotiators cut US trip short in new setback | Trump sanctions Iran's national bank | Survey finds Pennsylvania, Wisconsin lost the most factory jobs in past year Meghan McCain, Ana Navarro get heated over whistleblower debate MORE."

Trump shot back with several more tweets slamming Sanders for his endorsement of Hillary Clinton and inviting the Vermont senator's supporters to back the Trump campaign.

Sanders earlier Tuesday endorsed the presumptive Democratic nominee, effectively ending his own long primary campaign against Clinton.

“Secretary Clinton has won the Democratic nominating process, and I congratulate her for that,” Sanders said Tuesday.

“She will be the Democratic nominee for president, and I intend to do everything I can to make certain she will be the next president of the United States.”

In May, Sanders pressured Trump to debate him ahead of the California primaries, but Trump refused, saying it would be "inappropriate."

Trump has made several pitches to Sanders supporters in recent months, encouraging them to back his campaign instead of Clinton's.