Former Rep. Trey Gowdy (R-SC) has reportedly signed on to serve as outside counsel to President Donald Trump as part of his efforts to fight the House Democrats’ impeachment inquiry.

An unnamed administration official confirmed the move to the Associated Press on Tuesday evening.

Gowdy, who retired from Congress last year, represented South Carolina’s 4th Congressional District for eight years.

The former lawmaker served as House Oversight Committee chairman and oversaw the investigation into former Secretary of State Hilary Clinton and the events surrounding the 2012 terror attack in Benghazi, Libya. Since leaving Washington, D.C., Gowdy joined the law firm Nelson Mullins Riley & Scarborough and signed on as a Fox News Channel contributor.

The development came after the White House sent a letter to House Speaker Nancy Pelosi (D-CA) confirming it will not cooperate with the impeachment probe, branding it “illegitimate” and “unconstitutional.”

The letter, written by White House Counsel Pat Cipollone, accused the speaker of attempting to “overturn the results” of the 2016 presidential election.

“Given that your inquiry lacks any legitimate constitutional foundation, any pretense of fairness, or even the most elementary due process protections, the Executive Branch cannot be expected to participate in it,” the letter read. “Because participating in this inquiry under the current unconstitutional posture would inflict lasting institutional harm on the Executive Branch and lasting damage to the separation of powers, you have the President no choice.

“Consistent with the duties of the President of the United States, and in particular his obligation to preserve the rights of future occupants of his office, President Trump cannot permit his Administration to participate in this partisan inquiry under these circumstances,” it added.

Pelosi responded later Tuesday to President Trump with a letter of her own, vowing to hold him “accountable.”

“This letter is manifestly wrong, and is simply another unlawful attempt to hide the facts of the Trump Administration’s brazen efforts to pressure foreign powers to intervene in the 2020 elections,” the California Democrat wrote. “Despite the White House’s stonewalling, we see a growing body of evidence that shows that President Trump abused his office and violated his oath to ‘protect, preserve and defend the Constitution.”

“Mr. President, you are not above the law. You will be held accountable,” she concluded.

Pelosi kicked off the probe against President Trump late September after a partisan CIA officer accused the president in a so-called “whistleblower” complaint of asking Ukrainian President Volodymyr Zelensky to look into allegations of corruption against former Vice President Joe Biden and his son, Hunter Biden. Both have denied any pressure was applied to probe into the Biden family, and in a nod to transparency, the White House released a transcript of the presidents’ call to show no wrongdoing occurred.

On Tuesday, the Washington Examiner reported that the so-called “whistleblower” — who had been previously outed as a registered Democrat — in fact, had a previously “professional relationship’ with a 2020 Democrat White House hopeful.