Both former Texas Rep. O’Rourke and Minnesota Sen. Amy Klobuchar threw their support behind Biden at a campaign rally in Dallas on Monday, with Super Tuesday just hours away. Former South Bend, Indiana Mayor Pete Buttigieg, who ended his campaign on Sunday, also gave the former vice president his endorsement ahead of the campaign rally.

“Tomorrow, March 3, 2020, I will be casting my ballot for Joe Biden,” O’Rourke said at the Monday event. “We need somebody who can beat Donald Trump. The man in the White House today poses an existential threat to this country, to our democracy, to free and fair elections and we need somebody who can beat him and in Joe Biden we have that man. We have someone who, in fact, is the antithesis of Trump.”

“Joe Biden is decent, he’s kind, he’s caring, he’s empathetic,” said O’Rourke, who had been championed as a progressive candidate in the 2020 Democratic race. He later asserted that Americans “need Joe Biden.”

Not all appeared to agree, however, with multiple former O’Rourke staffers expressing disappointment in the former Texas representative’s pick.

Expressing her disappointment on Twitter, Katherine Fischer, a former staffer on O’Rourke’s 2018 Senate campaign, said she was “very sad to see this endorsement.”

Instead of following the former Texas representative’s lead, she said: “I hope Texas votes for Bernie Sanders tomorrow–he’s the candidate that Texans deserve.”

In an interview with Newsweek, Fischer, who now works for Turkish American journalist Cenk Uygur’s congressional campaign, said it was O’Rourke who first inspired her to enter the political world.

“I was doing something totally different in my life,” she said. However, when she heard O’Rourke speak, calling on Texans to embrace progressive policies, she felt compelled to join his campaign team.

“I had never seen anything like that in Texas before,” she said. “It was the first time I thought, as a Texan, there was maybe some hope for the state, that we could have better and more just representation and not just a string of people like Ted Cruz.”

Now, however, seeing O’Rourke embrace Biden’s campaign rather than supporting candidates with more progressive policies, Fischer said she and other staffers who were part of O’Rourke’s Senate campaign have been left “shocked and upset.”

“All of the Senate staffers I know would be quite shocked and upset,” she said.

In a separate statement published on Twitter, former staffer Ademali Sengal was among them, tweeting out: “I worked on@BetoORourke’s Senate and presidential campaigns. I’m incredibly disappointed that he is now endorsing @JoeBiden.”

“Beto got close to winning Texas as a progressive. Progressive values can and will win. That is why I support @BernieSanders,” said Sengal, who now appears to work with Flip the Senate, a campaign aimed at turning the Republican-led Senate blue.

Activist and journalist Shaun King said that he had “several former staffers” of O’Rourke’s contact him, with “some near tears, saying that his endorsement of @JoeBiden ‘felt like a betrayal’ of all they had worked for with Beto.”

“One said he loathed Biden’s campaign for President,” King said. “They just couldn’t make it make sense.”

Some former O’Rourke staffers sought to defend the former Texas representative’s decision, however, with one self-proclaimed former staffer, Devon Gray, writing in response to King’s post: “I can say with almost complete certainty that none of us would reach out to this guy to speak ill of our old boss.”

Meanwhile, Rob Flaherty, the digital director for Biden’s campaign and a former staffer for O’Rourke, simply said: “I’m thrilled!”

He also appeared to take aim at King, writing in a separate tweet: “Shaun King doing Hyperbole about people and situations he doesn’t like? Knock me over with a feather! Anyway, I love Beto and hate fake news provocateurs, so once again I’m on the right side.”

Fischer said that she believes there likely is a disparity in opinion between O’Rourke’s Senate and presidential campaign staffers when it comes to his decision to support Biden.

“I know there’s a lot of Beto’s presidential staffers who feel differently,” she said. “The presidential campaign was, you know, something that ran contrary to the way [O’Rourke] ran in Texas. He backed away from a lot of the progressive policies that he had endorsed and he had a very traditional team of people who have built their careers in the establishment. So, different teams and policies.”

Ultimately, Fischer said, “Beto’s endorsement won’t change my mind.”

“I will be voting for Bernie Sanders and I have been planning to do that for a while now.”

Newsweek has contacted both the Biden campaign and representatives for O’Rourke for comment.