Sanders supporters have launched a backlash against the former Democratic presidential candidate after he officially endorsed his opponent, Hillary Clinton, for president.

The Vermont senator appeared with Clinton, the presumptive Democratic presidential nominee, at a campaign event in New Hampshire and endorsed her while she stood by his side.

“Hillary Clinton will make a great president and I am proud to stand with her today,” Sanders said.

READ MORE: Sanders endorses Clinton: She is best candidate to address crises we face

A tirade of disappointed and angry comments poured in online as Sanders made his speech, with many feeling cheated and used by the self-described “democratic socialist.”

Boy, #BernieSanders is making #Hillary sound awesome. She would make one hell of a president if only any of it were true. — Lee Camp [Redacted] (@LeeCamp) July 12, 2016

Bernie Sanders, such a traitor. He made it known that he thought the election was rigged and corrupt. Now he endorses the most corrupt prsn — Joe Biggs (@Rambobiggs) July 12, 2016

Bernie Sanders is the new Dennis Kucinich.



(who? ...exactly!) — Max Keiser (@maxkeiser) July 12, 2016

Some commenters called Sanders’ turnaround disgusting and said it had pushed them to consider moving their support to the Republican party.

@BernieSanders I'm voting for trump he's the only hope this country has now STOP HILLARY — Ex Democrat!! (@BenBensmith4561) July 12, 2016

Presumptive Republican nominee Donald Trump also chimed in, accusing Sanders of selling out.

Bernie Sanders, who has lost most of his leverage, has totally sold out to Crooked Hillary Clinton. He will endorse her today - fans angry! — Donald J. Trump (@realDonaldTrump) July 12, 2016

I am somewhat surprised that Bernie Sanders was not true to himself and his supporters. They are not happy that he is selling out! — Donald J. Trump (@realDonaldTrump) July 12, 2016

Looks like @BernieSanders has sold his soul to the devil, #CrookedHillary. Everything he is supposed to stand against. SAD! #SelloutSanders — Ivanka Trump (@reaIIvankaTrump) July 12, 2016

Hillary Clinton thanked her former rival for the endorsement, highlighting his contribution to fighting injustice.

Sanders had been reluctant to bow out of the race but had changed his sentiment in recent weeks, insisting that the most important thing now was to defeat Trump and elect Clinton.

Thank you, @BernieSanders, not just for your endorsement, but for a lifetime of fighting injustice. — Hillary Clinton (@HillaryClinton) July 12, 2016

"Hillary Clinton will make an outstanding president, and I am proud to stand with her today." —@BernieSanders — Hillary Clinton (@HillaryClinton) July 12, 2016

Meanwhile, Sanders posted a comment to his Twitter page, saying the focus must now be to see through a Democratic platform and a Clinton presidency.

The remarks are a sharp turnaround from his previous opinions of Clinton, who he once said was “not qualified to be president.”

Our job now is to see our progressive platform implemented by a Democratic Senate, a Democratic House and a Hillary Clinton presidency. — Bernie Sanders (@BernieSanders) July 12, 2016

The post was met with a barrage of critical comments as Bernie Sanders quickly shot his way up to the top of US Twitter trends, with #SelloutSanders, #ByeByeBernie and #NeverHillary among the hashtags being used.

@BernieSanders so all that shit you said about @HillaryClinton before was just BS? — ❥ (@VeeVee) July 12, 2016

@BernieSanders I'm deeply ashamed of you for abandoning your principles this easily. You were better than that. #ByeByeBernie — Charles Baker (@CharlesEbaker) July 12, 2016

@BernieSanders Is this you regretting you sold your soul to Satan? pic.twitter.com/7IsWQ1Mr8W — T. Lindh (@LindTuo) July 12, 2016

Bernie Sanders is a sell out pic.twitter.com/ikAzyKIqCJ — Liberty Hangout (@LibertyHangout) July 12, 2016

Bernie Sanders can try and paint some lipstick on the pig, but Corrupt Crooked Hillary's still a pig pic.twitter.com/xSOuGMX1BV — Ian56 (@Ian56789) July 12, 2016

Bernie Sanders endorsing Hillary Clinton feels so much like when the girl you love starts dating the guy you hate most. — Dan LaMorte (@DanLaMorte) July 12, 2016