Editor's note: This story has been updated with comment from U.S. Rep. Raul Grijalva.

WASHINGTON — The festering anger in the Democratic nomination fight spilled over into the unofficial vice presidential selection process Tuesday, as a coalition of liberal groups attacked the record of Housing and Urban Development Secretary Julián Castro. 

The groups are targeting Castro "on the relatively obscure issue of his handling of mortgage sales," according to Politico. The coalition charged that in his capacity in the Cabinet, Castro favored private equity firms over minority populations. 

The point of the charges was "to publicly discredit Castro as a progressive, latching onto the mortgage issue to seed enough suspicion to keep him off Clinton’s short list," the article stated. 

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The coalition also launched a website to collect names for a petition to be sent to Castro's office.

"Secretary Castro is widely seen as a rising political star and many people think he is destined for higher office in Washington," the site reads. "But first he needs to fulfill his mission as the leader of HUD and stabilize communities by refusing to sell our neighborhoods away to Wall Street for a discount."

As the Democratic contest between former Secretary of State Hillary Clinton and Vermont Sen. Bernie Sanders becomes more embittered by the day, Castro has been widely viewed as being on Clinton's shortlist for running mates. He was an early backer of Clinton and campaigned hard for her in February in the lead-up to the March 1 Texas primary. 

America Rising, a GOP opposition research shop, highlighted Tuesday's news as proof that Democrats are in disarray. 

"Secretary Castro has practically been inaugurated as Vice President without even the most cursory vetting," spokeswoman Amelia Chassé said. "Now it appears that Secretary Castro's record is finally facing scrutiny and has been found wanting by a Democratic Party that continues to lurch toward socialism."

Both the Politico story and the coalition's website quoted a critical letter to Castro penned by U.S. Rep. Raul Grijalva, an Arizona Democrat and is one of eight members of Congress who has endorsed Sanders.

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Grijalva clarified to The Texas Tribune that his intent was to encourage Castro to change course on the policy and to promote "reinvestment in the poor neighborhoods" of his Tucson-based district. He emphasized that his criticism was about a specific policy, and not about Castro's potential as a national political figure.

"It wasn't intended to scuttle or torpedo whatever is in the future for the secretary," he said of the vice presidential speculation.

Castro allies back home were also quick to defend him.

"From the perspective of Texas Democrats and our chairman, Gilberto Hinojosa, Julián Castro is  immensely prepared, qualified and ready to deliver progressive change for families across the country and to be vice president of the United States," said Texas Democratic Party Deputy Executive Director Manny Garcia.

Congressional candidate Pete Gallego, a former U.S. House member who is challenging Republican U.S. Rep. Will Hurd for the 23rd Congressional seat, also weighed in. 

"I'm a Democrat, but I'm not afraid to call out people from my own party when they're wrong, and they're dead wrong on this. Julian Castro is an accomplished leader who embodies the hopes and dreams of many younger Americans," Gallego said. "Julian Castro would be a phenomenal vice presidential nominee for our party as well as a great vice president for our country." 

Young and Latino, Castro would likely be adept at energizing groups that Democrats need to turn out in the fall. But also, Texas Democrats pin much of their future on Castro and his twin brother, U.S. Rep. Joaquin Castro of San Antonio, and hope that the national party could make inroads in Texas if Clinton tapped the former San Antonio mayor as her running mate.

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