“The letter’s constitutional and ‘legal’ arguments are baseless,” former Obama White House counsel Bob Bauer wrote. “It misrepresents the constitutional law and precedent that it is pleading on the president’s behalf. On the merits, it is an exceptionally weak performance.”

In the letter, Cipollone contended the House’s procedure was fatally flawed because it had not been approved by a floor vote. “Your contrived process is unprecedented in the history of the nation, and lacks the necessary authorization for a valid impeachment proceeding,” the White House counsel wrote.

Despite the intense criticism, even ridicule that Cipollone’s letter received, Engel’s memo — which runs to 37 pages in the version the White House released and 54 in the format issued by DOJ — reaches the same conclusion.

Some of those who skewered Cipollone over the Oct. 8 letter said they would view it as less objectionable if he actually had some opinion from the Justice Department at the time supporting the aggressive positions he staked out.

“The OLC opinion is certainly better argued than the earlier Cipollone letter. It is more sober in tone, and more serious in its analysis,” said Keith Whittington, a Princeton University politics professor who joined in the earlier criticism.

“It is a pity the White House did not produce a document of this sort when it was first responding to the House inquiries. If it had done so, the president might have avoided the second article of impeachment and created a meaningful framework within which the House and White House could have negotiated some level of cooperation — or at least clarified the reasonable obstacles to cooperation,” Whittington added.

Other critics said it was still not clear whether Cipollone knew about Justice’s position before he fired off his combative message to the Hill. The Justice Department did not immediately respond to questions about the timing or form of the advice DOJ lawyers rendered last October.

“It is not apparent there was anything in writing or even that it had been provided as of the time of the Oct. 8 letter,” said former House attorney Michael L. Stern.

However, Whittington and Stern also noted that while Cipollone’s letter included the straightforward claim that the House needed to vote on impeachment before subpoenaing people or demanding documents, the White House counsel also made a variety of other arguments that the House’s process was unconstitutional.

Stern said it appeared Cipollone was actually soft-pedaling the point about the House needing to vote, because it was so “easily cured.” Indeed, the House did just that about three weeks later as it voted almost entirely along party lines, 232-196, to formalize the impeachment inquiry.

Some lawyers said the memo vindicated or at least buttressed Cipollone's position.

"Cipollone’s letter, and the underlying OLC opinion, are entirely correct," said David Rivkin, a Justice Department official during the Reagan and George H.W. Bush administration's. “While the House eventually complied with its obligations, its initial effort to commence the impeachment inquiry without taking a vote underscores its disregard of the constitutionally-required procedures."

If Cipollone had the Justice Department’s advice before he wrote the Oct. 8 letter, it’s not clear why he didn’t mention that. One possibility is doing so might have caused a clamor for an immediate, formal DOJ opinion in a very fluid situation.

Another is that announcing that DOJ was staking out such an arguably extreme position on that point might have undercut the arguments Justice Department lawyers were presenting in various court fights related to demands for Trump’s financial records, grand jury records from the Mueller probe and testimony from former administration officials on various topics.

For instance, on Oct. 1, Justice Department lawyers filed a brief saying the courts should hold off ruling on a House suit to enforce a subpoena against former White House counsel Don McGahn because efforts at accommodation should be given time to work. However, that position seemed to be undercut by Cipollone’s letter a week later signaling a stiff-arming of Congress. By the end of the month, DOJ gave up on the argument that more time was needed for “accommodation” between the branches.

Just three days after the White House counsel’s caustic letter, the D.C. Circuit Court of Appeals ruled in a case about a subpoena for Trump’s financial records. That ruling did not center on impeachment, but the dissenting judge on the three-judge panel, Trump appointee Neomi Rao, said she believed the Constitution requires a full vote of the House before going after records directly related to the president.

The Justice Department opinion released Monday includes at least nine citations to Rao’s dissent, although it was not issued by the time of Cipollone’s letter and may not have been available to OLC when it was first approached.

It is not unusual for OLC, whose legal advice is typically the last word within the Executive Branch, to issue informal opinions by phone or email and to follow up weeks or months later with a formal opinion.

“There are a lot of different ways in which OLC gives advice. A very small piece of that is writing formal opinions,” acting OLC chief Karl Thompson said in remarks reported by POLITICO in 2015. “The vast majority of our advice is provided informally — is delivered orally or in emails. That is still authoritative. It is still binding by custom and practice in the executive branch. It’s the official view of the office. People are supposed to and do follow it.”

Some officials said at the time that requests for formal opinions were on the decline because of concerns release of such opinions might be forced under the Freedom of Information Act. However, courts have been less friendly to such efforts in recent years.

Metadata attached to the Justice Department’s version of the opinion appears to link the document to Nate Forrester, an OLC attorney who also worked in that office during the George W. Bush and Obama administrations. Forrester also served as a law clerk to Supreme Court Justice Anthony Kennedy and as Alabama solicitor general. A Justice official said Forrester is a career lawyer in charge of preparing OLC’s opinions for formal publication and handled that aspect of the release.