WASHINGTON — Julián Castro’s allies are boiling over criticism of the Housing and Urban Development secretary from progressive corners, characterizing the attacks as political shrapnel from the ongoing fight between Hillary Clinton and Bernie Sanders blocs of the Democratic Party. 

An alliance of liberal groups unloaded on the former San Antonio mayor Tuesday in a Politico article and in a petition drive, charging him with siding with Wall Street banks over struggling families with distressed mortgages.

But Democratic officials from Austin to Washington say the push is the party's anti-establishment liberal base tearing down Castro to assert its will onto party frontrunner Clinton’s vice presidential selection process. 

To be sure, the former U.S. senator and secretary of state has yet to clinch the nomination, but Sanders has an uphill climb to secure enough delegates to overpower her. 

“I don’t know exactly what the motivation is behind this," said U.S. Rep. Ruben Gallego, an Arizona Democrat. "I think, unfortunately, whatever their aim was, it ends up looking more political than anything else ... if the goal was a policy end, they detracted from their policy end by making this an inherently political issue." 

Within hours of the article posting on Tuesday, those jumping to Castro's defense included Democratic U.S. House candidate Pete Gallego of Texas, a left-leaning policy group called Progress Texas, the Latino Victory Fund and the Texas Democratic Party.

The article enraged many Democrats at the U.S. Capitol as well, including a handful of Congressional Hispanic Caucus members who declined to speak openly about their ire. 

The petition charged that HUD promised to avoid foreclosures by selling mortgages to nonprofits in lieu of large banks. The coalition argues that HUD has not lived up to those promises, and the groups' website called for Castro to "stop selling our neighborhoods to Wall Street."

A complaint U.S. Rep. Raul Grijalva of Arizona wrote to Castro on the issue was quoted in the piece. On Tuesday, Grijalva aimed to distance himself from the vice presidential politics.

Democratic Conference Chairman Xavier Becerra, a California congressman and the highest-ranking Latino in Congress, praised Castro when asked about the criticism on Wednesday. 

“Secretary Castro has done a great job, masterful job as secretary, and he’s been a talent here in Washington, D.C.,” Becerra he said. “I’m not sure what much more I can say.” 

The dispute emerges as Democrats are increasingly at each other’s throats as Clinton and Sanders battle for the party nomination. 

Some Democrats speculate the anti-Castro petition drive is a bid to deep-six the chances of the longtime Clinton loyalist to become her running mate — while boosting the positioning of liberal base favorites like U.S. Sen. Elizabeth Warren of Massachusetts or U.S. Labor Secretary Tom Perez. 

Several Hispanics in state and national politics were incensed to see the left undercut a Latino who has a viable shot at higher office.

"A lot of people, certainly, I’ve talked to here find it distasteful," said Ruben Gallego, the Arizona Democrat. 

And a spokesperson at HUD also pushed back, saying that the department is committed to "providing an option for homeowners to remain in their homes."

"We’ve received feedback from stakeholders, which has led us to make a number of important changes to the program, including the creation of nonprofit-only pools and delaying foreclosure for a year," he added. 

Politico named 13 groups involved in the petition: Alliance of Californians for Community Empowerment (ACCE) Action, American Family Voices, Color of Change, Courage Campaign, CPD Action, Daily Kos, MoveOn, New York Communities for Change, The Other 98%, Presente, RootsAction, Rootstrikers and the Working Families Party.

But of the groups returning calls from the Tribune, representatives mostly avoided the charged political language in the original article. Two spokespeople argued the conflict was not about who will be the next Democratic vice presidential nominee. 

"I just don’t think that’s right," said Amy Schur of ACCE Action. "The need for decent, affordable housing is a tremendous crisis, and a lot of progressive organizations recognize the importance of that issue." 

She called the program at HUD "broken." 

"Castro happens to be the head of this federal agency, so should be no surprise he’s getting the flak for this program that’s hurting communities," she added. 

"I would say it’s to be expected and an indication that people are hearing us, and that’s somewhat encouraging," David Swanson of RootsAction.org, said of the blowback. "There shouldn’t be this kind of pushback, but it’s predictable." 

He, too, insisted this was all about reform in the mortgage market. 

"That’s the issue for us," he added. "It doesn’t have anything to do with making somebody a vice president." 

Matt Nelson of Presente, a Latino progressive group, did question Castro as a vice presidential contender in the original piece, calling him a "toxic asset" for Clinton.

"What rings hollow is to say that we can’t hold Mr. Castro accountable because he's Latino," he said. 

But Jason Stanford had a far different view, arguing the progressive attacks might actually boost Castro’s chances.  

A former operative for Castro and his twin brother, U.S. Rep. Joaquin Castro of San Antonio, Stanford now works in the Austin mayor's office. “Let’s assume that Secretary Clinton gets the nomination,” he said, speaking from the perspective of a longtime Democratic strategist. “Now if she doesn’t pick Castro, it’s going to look like this had an effect. I don’t see how this works out for them.” 

“She’s not going to want to look weak when she’s running for president, and the Clintons are kind of good at politics,” he elaborated. 

And, he cautioned, politics involving Castro is unique, thanks to his identical twin brother in the U.S. House. 

“You take out one, we have a spare,” he joked.