(CNN) - Internal Revenue Service chief John Koskinen's own political leanings are coming into question as the controversy continues to unfold involving the agency’s targeting of certain political groups.
Over the past 30 years, Koskinen has given more than $100,000 to Democratic causes, according to FEC filings. But the government veteran downplayed his political activity, telling CNN's Wolf Blitzer on Thursday, "I've never been a partisan operative, a political operative."
"I was actually asked by the Bush administration to come in and work on Freddie Mac," he said in an interview that aired on "The Situation Room."
The IRS controversy became more convoluted last week when the agency announced the destruction of e-mails from former IRS official Lois Lerner, lost in an apparent hard drive crash.
The agency did not reveal for months that Lerner's emails had been lost - stirring further Republican outrage with the agency and calling into question its officials' credibility in the investigation.
House Republicans on Friday called for more documents and information from the Obama administration about the circumstances surrounding the missing documents.
“We still can’t get straight answers from the IRS or this administration about the circumstances of the destroyed IRS e-mails," House Ways and Means Chairman Dave Camp and Rep. Charles Boustany of Louisiana said in a statement.
"And, we now know that the IRS, Treasury and White House knew that years’ worth of Lerner emails conveniently were destroyed, yet kept it secret from Congress. This administration needs to live up to the transparency and openness it promised, and give this committee all the documents it needs to complete its investigation,” the statement said.
Republicans are calling on Attorney General Eric Holder to appoint a special prosecutor to investigate the agency over the missing e-mails.
Asked by Blitzer whether a criminal investigation was warranted, Koskinen replied: "I don't think ... at this time there's any evidence of that."
Democrats, meanwhile, are accusing House Republicans of politicizing the IRS investigation, noting that some liberal groups seeking tax-exempt status also apparently were targeted by the agency.
CNN's Dana Davidsen, Tom Cohen and Tom Foreman contributed to this report.