The Republican House Oversight chairman argued in a scathing letter to the leading Democrat on his panel Friday that the pursuit of contempt charges against former IRS official Lois G. Lerner is justified.

House Oversight and Government Reform Committee Chairman Darrell Issa's letter to Elijah Cummings, of Maryland, rejected a claim made this week by Cummings that the panel had no right to pursue contempt charges against Lerner because it had not officially rejected her claim against self-incrimination.

Issa also criticized Cummings' recent public takedown of the chairman over the Lerner matter, calling him, “an obstacle to effective Congressional oversight," and a “defense counsel for Lerner and others who act to deprive Americans of their constitutionally-guaranteed rights.”

Lerner invoked the Fifth Amendment when she refused on two occasions to testify before the panel about her involvement in the IRS' additional scrutiny of Tea Party groups seeking tax-exempt status.

Cummings has argued that the GOP’s pursuit of a contempt charge against Lerner is politically driven and lacks legal standing.

The top Democrat on the panel reacted angrily at a March 5 hearing when Issa refused to allow Cummings to respond to Issa's criticism of Lerner after she refused to testify for a second time.

On March 12, Cummings sent a letter to House Speaker John Boehner, R-Ohio, making his case against Issa.

On Friday, Issa responded, taking a personal jab at Cummings along the way.

“Even though the White House helped orchestrate your ascension as ranking member,” Issa wrote, referring to reports that Democratic leaders allowed Cummings to leapfrog a more senior lawmaker on the advice of the Obama administration, “I have encouraged you to subordinate your political loyalties to the institutional interests of the Committee and the House, especially in cases like this where obstructing the committee’s work risks permanently disadvantaging Congress in its interactions with the executive branch.”

Cummings, in his letter to Boehner last week, said constitutional law experts concluded Issa committed a “fatal error” at the end of the March 5 hearing by following the rules required to hold a person in contempt of Congress.

Cummings gave the Washington Examiner a response to the Issa letter:

“Not two, but seven independent Constitutional law experts have now concluded that Chairman Issa botched the contempt proceedings. The Chairman’s letter today provides no House Counsel memo or opinion, even though he and Speaker Boehner claimed they had one this week, and it cites no experts who support his inaccurate view of the Constitution and the law. The entire country has now seen firsthand how Chairman Issa runs this Committee in violation of House Rules, and no reasonable person would accept his legal views over those of the United States Supreme Court. Contrary to Chairman Issa’s accusations, we are not defending Lois Lerner or her actions — we are defending the Constitution and the rights it guarantees to all Americans.”

Issa contents that the committee made it clear to Lerner that they believed she had waived her Fifth Amendment right to remain silent when she delivered testimony in her own defense at an Oversight hearing last year. Issa said the press also reported the committee vote rejecting her Fifth Amendment claim.

“Accordingly, it is facially unreasonable for you and your lawyers and your consultants to now claim that “at no stage in this proceeding did the witness receive the requisite clear rejections of her constitutional objections,” he said.

Darrell Issa's letter to Elijah Cummings