The eight-page letter reads more like a political document than a legal one, echoing many of President Donald Trump’s claims about the House Democrats who are investigating him. It also calls on Democrats to dismantle the process they set up to impeach Trump over allegations that he abused his power by pressuring Ukrainian leaders to help discredit his political rivals.

The Trump administration’s latest assault on House Democrats’ myriad investigations sets up yet another constitutional clash between the executive and legislative branches — one with far-reaching implications over the powers of the presidency and of Congress.

“All of this violates the Constitution, the rule of law, and every past precedent. Never before in our history has the House of Representatives — under the control of either political party — taken the American people down the dangerous path you seem determined to pursue,” Cipollone added.

In particular, Cipollone took issue with the fact that the House has not formally voted to authorize the establishment of an impeachment inquiry, calling it a violation of due process.

“In the history of our nation, the House of Representatives has never attempted to launch an impeachment inquiry against the president without a majority of the House taking political accountability for that decision by voting to authorize such a dramatic constitutional step,” he wrote.

Cipollone also echoed Republicans’ criticisms of House Intelligence Committee Chairman Adam Schiff (D-Calif.), whose staff had previous contact with the whistleblower who first sounded the alarm about Trump’s July 25 call with Ukrainian President Volodymyr Zelensky, during which Trump pressured Zelensky to investigate former Vice President Joe Biden.

“Anyone who was involved in the preparation or submission of the whistleblower's complaint cannot possibly act as a fair and impartial judge in the same matter — particularly after misleading the American people about his involvement,” Cipollone wrote.

He accused Democrats of threatening witnesses by suggesting in recent correspondence that a refusal to comply with their impeachment inquiry would be treated as evidence of “obstruction.”

In response, Pelosi reissued that threat and said Cipollone was seeking to “cover up [Trump’s] betrayal of our democracy.”

“The White House should be warned that continued efforts to hide the truth of the president’s abuse of power from the American people will be regarded as further evidence of obstruction,” Pelosi said in a statement. “Mr. President, you are not above the law. You will be held accountable.”

The White House’s argument may already be in legal trouble. The chief judge of Washington's federal district court indicated earlier Tuesday in a related proceeding that she gives great “deference” to the House’s authority to devise its own impeachment procedures.

The judge, Beryl Howell, repeatedly challenged the Trump administration’s view that a formal vote is necessary to declare an impeachment inquiry — though she conceded it would be a more clear-cut call if a vote occurred. Howell is expected to rule later this month on whether the House’s impeachment probe is legitimate and warrants the release of special counsel Robert Mueller’s grand jury materials to Congress.

Trump’s GOP allies on Capitol Hill have pushed Pelosi to hold a vote, but she has maintained that such a vote is unnecessary because it is not outlined as a requirement in the Constitution.

“No court and certainly no executive branch agency has the constitutional power to tell the legislative branch it is or is not formally in an impeachment inquiry,” Rep. Gerry Connolly (D-Va.), a senior member of the House Oversight and Reform Committee, said in an interview. “If we say that’s what we’re doing, that’s what we’re doing.”

The document includes few defenses of Trump’s phone call with Zelensky, which is at the heart of the House’s impeachment inquiry. While Cipollone wrote that “the call was completely appropriate,” his letter focuses mostly on the impeachment process itself.

The White House’s memo comes just hours after the State Department intervened to block Gordon Sondland, the U.S. ambassador to the European Union, from testifying before the three House committees that are leading the impeachment inquiry.

Democrats, including Schiff, have indicated that outright stonewalling from the White House could compel Democrats to move forward with articles impeachment based on obstruction of their investigation.

“They say: they will not cooperate with an impeachment inquiry unless it’s on their terms. They mean: the president is above the law,” Schiff wrote on Twitter shortly after Cipollone’s letter was released. “The Constitution says otherwise.”

The president’s posture toward House Democrats’ investigations as outlined on Tuesday is not new; earlier this year, Trump declared that he would ignore all congressional subpoenas, and his administration has subsequently ignored several subpoenas, refusing to provide documents while blocking witnesses from testifying.

“This is really nothing but a political strategy because Democrats want to overturn the results of the 2016 election, and they want to use impeachment and the political strategy to influence the results of the 2020 election,” said a senior administration official.

The White House is hoping to bring into the fold Trey Gowdy, a former South Carolina GOP congressman and chair of the House Oversight Committee who was at the White House on Tuesday, where he met with acting chief of staff Mick Mulvaney and others about potentially joining Trump’s legal team as an outside adviser. Gowdy did not return a call seeking comment.

Cipollone has also argued that the House should, in keeping with previous impeachment efforts, authorize the Republican minority to subpoena witnesses, as well as allow witnesses enough time to prepare for depositions.

The White House letter did not indicate that Trump intends to invoke executive privilege to block the House’s access to witnesses or documents. Cipollone indicated that the White House would be open to working with Democrats if they shelved their impeachment push and instead focused on the “regular order of oversight requests.”

Trump invoked executive privilege in May to block Congress from accessing elements of Mueller’s report on the Trump campaign’s contacts with Russia in 2016. He did it again in June, when Congress was seeking documents and testimony about the administration’s handling of the 2020 Census.

But more often, witnesses and White House officials have muzzled themselves, claiming that they can’t reveal details of their conversations and interactions with Trump because of the potential they could breach his right to confidentiality. Democrats have rejected this claim as an inappropriate expansion of executive privilege.

The White House has also claimed that former senior advisers to the president have “absolute immunity” from testifying to Congress — an even more sweeping effort to block cooperation.

Heather Caygle and Nancy Cook contributed to this report.