(CNN) -- Just when it seems impossible for things to get uglier between the two heads of a key House investigative committee, they have. Hours after Democrat Elijah Cummings accused House Oversight Chairman Darrell Issa of engaging in "McCarthyism," Issa shot back with a letter to Cummings accusing him of obstructing the committee's IRS investigation, and even contributing to the agency's targeting of conservative grass roots groups. "New IRS documents identified by the committee raise disturbing concerns about your possibly motivations for opposing this investigation and unwillingness to lend your support to efforts to obtain the testimony of former IRS exempt Organizations Director Lois G Lerner," Issa wrote to Cummings.
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House panel to vote Thursday whether to hold former IRS official Lois Lerner in contempt
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Republican Darrell Issa of California is chairman of the House Oversight Committee
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The panel's top Democrat, Rep. Elijah Cummings, says it's a tactic worthy of McCarthy
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Sen. Joseph McCarthy's anti-communism efforts are seen as a dark page in U.S. history
Elijah Cummings
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Elijah Cummings
@placeholder points out that he only requested public information from the IRS, and that he posted his inquiry to True to the Vote on his website -- so he wasn't hiding anything.
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March: @placeholder agrees to hand over Lerner's e-mails to Issa
Darrell Issa
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Darrell Issa
March: IRS agrees to hand over Lerner's e-mails to @placeholder