U.S. Attorney General Eric H. Holder Jr. has declined to appoint a special prosecutor to investigate the Internal Revenue Service’s targeting of advocacy groups for extra scrutiny based on their policy positions.

Holder announced the decision in a letter last week to Sen. Ted Cruz (R-Tex.), saying that “such an appointment is not warranted” because the case does not present a conflict of interest.  Cruz had requested an independent investigation in January.

The attorney general said in his response to the senator that “career prosecutors and law-enforcement professionals” were conducting the Justice Department probe. “The Department remains committed to integrity and fairness in all of its law-enforcement efforts, without regard to politics,” Holder said.

Cruz criticized the decision on Thursday, saying in a statement that Holder “has chosen to reject the bipartisan tradition of the Department of Justice of putting rule of law above political allegiance.” He cited past examples in which attorneys general appointed special prosecutors to investigate Watergate under President Richard Nixon and the Monica Lewinsky scandal under President Bill Clinton.

In his January request, Cruz said an independent investigation was necessary because the Justice Department had not indicted anyone for the IRS behavior and because one of the prosecutors helping to lead the DOJ probe had donated heavily to President Obama and the Democratic party.

Many Republicans, including Cruz, have suggested that the IRS targeted mainly conservative groups for additional scrutiny as part of an effort to stifle Obama’s critics during the past two election cycles.

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