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Arizona Democrat says some senators urging him to challenge Sinema with party at a 'breaking point'

(CNN) Rep. Ruben Gallego says his phone has been ringing a lot recently -- with many Democrats making a pitch to him: Run against Arizona Sen. Kyrsten Sinema in 2024.

Among those making the case, he claimed, are Sinema's own Senate Democratic colleagues.

"It wasn't Bernie, I'll tell you that," Gallego told CNN, referring to Vermont independent Sen. Bernie Sanders, who has said he's open to backing a primary challenge to Sinema.

"It's more than one" senator, he added before declining to say which of Sinema's colleagues are privately hoping she will face an intraparty fight.

And he said that in the last several days the courtship has only intensified.

"To be honest, I have gotten a lot of encouragement from elected officials, from senators, from unions, from your traditional Democratic groups, big donors," said Gallego, a seven-year House veteran. "Everything you can imagine under the sun."

It's rare for senators to back primary foes against someone from their own party, but there has been escalating tension over the role that Sinema and West Virginia Sen. Joe Manchin have played in holding the line against the wishes of their progressive colleagues.

The most recent episode came on Wednesday night, when the two centrist Democrats voted with all Republicans to maintain the Senate's 60-vote threshold to overcome a filibuster on legislation, effectively torpedoing their party's ambitious plans to rewrite the nation's election and voting laws. Both senators backed the election legislation but said the filibuster must be maintained to prevent future Senate majorities from working their will over the minority party.

Sinema and Manchin also drew the left's ire by drawing a line against the $3.5 trillion price tag for President Joe Biden's Build Back Better plan, effectively slicing that proposal in half. And while it was Manchin who ultimately slammed the brakes on Biden's bill, Sinema forced the party to rewrite its proposal to increase tax rates on wealthy individuals and corporations, angering liberals by her stance.

Hours before Biden came to Capitol Hill for a final pitch to Senate Democrats on his voting bill last week, Sinema went to the floor to reiterate her long-standing opposition to gutting the 60-vote threshold to allow just 51 votes to advance legislation.

"And while I continue to support these bills, I will not support separate actions that worsen the underlying disease of division infecting our country," she said at the time.

In an interview Thursday, Gallego said the last few weeks have amounted to a "tipping point situation" among many in his party since there's been "a whole lot of frustration over a lot of things that have occurred in the past with Sen. Sinema, and this has kind of been the breaking point."

Sinema, who won her first term in 2018, could be vulnerable in a primary, said Gallego, who will make a decision on whether to challenge her next year.

"I think she's vulnerable because nobody in the state has seen hide nor hair of her for the last three years," he said.

And then the potential challenger unloaded.

"She hasn't had one town hall; everything she does is scripted," he said. "She says she refuses to negotiate in public, but we want to know who is she negotiating for? Is it for Arizonans? Or is it for the pharmaceutical companies or whatever other interests that she is more likely to have meetings with than it is with the actual constituents?"

Sinema's office shrugged off Gallego's comments but provided CNN a list of her meetings with constituents in recent weeks. Her office disputed the idea that she hasn't been visible in Arizona, noting she's had tele-town halls given that in-person town halls are rare during the coronavirus pandemic.

"Sen. Sinema and our team have recently held numerous virtual and in-person meetings with Arizona civil rights leaders, Arizona student groups, Arizona tribal leaders, Arizona military leaders, progressive leaders, Arizona local elected leaders and more," her office said.

On Thursday, some of Sinema's critics were still reeling from her stance over the filibuster.

Sanders, who caucuses with Democrats, called Gallego a "very good congressman," though he said it was "a little bit early" to talk about primary challenges in the next cycle.

"These are people who I think have undermined the President of the United States," Sanders said of Manchin and Sinema, adding: They "can expect to find primary challenges" in 2024.

"They have forced us to have five months of discussions that have gone absolutely nowhere," Sanders said of his two moderate colleagues.

Leaving a Senate vote on Thursday, Manchin said he's prepared for a 2024 primary challenge -- and didn't seem too concerned about Sanders' comments.

"I'm not a Washington Democrat, so the base they have is a different base than I have," Manchin told CNN.

Asked about Sanders, he added: "That's life today. That's life in politics today. I never believed that's a team sport."

CNN's Morgan Rimmer contributed to this report.