Since President Barack Obama announced the nomination of Tom Perez to be the nation's next Labor Secretary, Republicans have begun preparing for a fight over Perez's history as the Justice Department's assistant attorney general for civil rights.

House Oversight Committee Chair Rep. Darrell Issa and Sen. Chuck Grassley (R-Iowa) have led the preemptive charge against Perez, which rests mostly on a Minnesota housing discrimination case he helped prevent from going to the Supreme Court.

Republicans have also latched onto a few other items of Perez's work at the Justice Department. On Monday, Rush Limbaugh said he "may as well be Hugo Chavez," referring to a dropped case regarding the New Black Panther Party. Perez has also been involved in numerous civil rights-related investigations, including one into Trayvon Martin's death, and in various voter ID law challenges.

But where Perez's opponents will likely get the most mileage is in the case of Magner v. Gallagher. The case was dismissed in February 2012, which serves as the basis for its controversy.

The conservative editorial board of the Wall Street Journal has led the charge on this issue over the past few days.

In a lengthy editorial on Tuesday, the Journal reviewed Perez's involvement on the case.

The case revolved around the legality of "disparate impact," a provision of the Fair Housing Act of 1968 that makes it illegal for local governments to enforce the housing code in a manner that negatively affects minority groups, regardless of the intent of bias.

The disparate impact defense has held up throughout lower-level and appeals courts for nearly 40 years as part of the Fair Housing Act, but city officials in St. Paul, Minn., appealed to the U.S. Supreme Court.

The conventional wisdom about the case was that the Supreme Court, led by Chief Justice John Roberts, would strike down the disparate impact defense for the same reasons that it reversed precedent on Citizens United and looks likely to strike down the Voting Rights Act. "Disparate impact," specifically, does not appear in the language of the Fair Housing Act, and many of the court's conservative-leaning justices employ a "plain-language" view of the law.

That's where Perez comes into the story. The Journal explains:

On November 17 [2011], Mr. Perez emailed a former colleague, Thomas Fraser at the Fredrikson & Byron law firm in Minnesota, to probe if city officials might be convinced to withdraw Magner, according to documents that the Justice Department sent to Congressional investigators. Mr. Fraser referred Mr. Perez to his colleague, David Lillehaug, who was advising St. Paul on a pending False Claims Act case against the city filed by a private citizen.

Mr. Perez had stumbled onto a potential quid pro quo: The feds could decline to intervene in the false claims case (known as Newell) in exchange for the city withdrawing Magner from the Supreme Court.

Republicans leading the opposition charge that Perez's involvement in the case amounts to "corruption" and bribery. But Democrats have brushed those charges aside as more GOP obstruction, pointing out that the Inspector General did not mention the case in a 2013 review of the Justice Department's Civil Rights division.

“It was the wrong thing to do,” Sen. Jeff Session (R-Ala.) told Bloomberg. “It was a highly important legal issue that he was afraid he would lose, so he basically created an incentive — some might call it a bribe — for a city not to pursue this legal case.”

For his part, Frederick Newell, the defendant in the Newell case the Justice Department agreed to drop, told Bloomberg that he felt cheated out of millions of dollars he stood to gain from whistle-blowing on the alleged misuse of job-assistance funds in St. Paul.

Tim Iglesias, a law professor at the University of San Francisco who specializes in housing and property law, acknowledges that the case "can be made to look bad" on the surface. But in reality, he doesn't see anything improper about the quid pro quo.

"The idea of the government bargaining with a party to get something else is not uncommon. It's not a huge, big deal among legal professionals," Iglesias told Business Insider.

"Of course, it can be made to look bad. But if you look at what goes on day by day to make our system work, this kind of thing goes on all the time."