“The [Treasury Inspector General] inquiry determined Treasury’s receipt, handling, and responses to Chairman Neal’s letters and requests followed the general process with the occasional change in Treasury officials involved,” Luttrell wrote.

In a separate letter to Neal and Rep. Kevin Brady, the top Republican on Ways and Means, acting Treasury Inspector General Richard Delmar said the investigators “do not presume to opine” on the legal basis for the decision to withhold Trump’s returns, which followed advice from the Justice Department’s Office of Legal Counsel.

“We report the Treasury decision to conform to that advice, and do not have a basis to question that decision,” Delmar wrote.

Erin Hatch, a spokeswoman for Neal, said he “maintains that the law is on his side and he believes his request should be granted."

Neal has argued that he needs access to Trump’s returns to examine how thorough the IRS is in its routine audits of presidents, and he has cited a law that requires the Treasury secretary to turn over returns requested by the chairs of Congress’s tax committees.

However, Democrats also have long been interested in combing Trump’s returns for any evidence of wrongdoing.

Mnuchin maintains that Neal needs a legitimate legislative reason to obtain the returns and doesn’t have one.

Delmar's decision not to weigh in on Treasury’s legal reasoning is notable because the validity of OLC decisions is a matter that has increasingly been thrown into doubt by judges who have ruled that OLC opinions don't carry the force of law.

Most recently, the chief judge in Washington, D.C.'s federal district court, Beryl Howell, cast skepticism over OLC's claim that a sitting president cannot be indicted. And other inspectors general have at times treated OLC opinions as advisory, rather than binding.

In addition, Delmar is one of a handful of temporary inspector generals, performing the role while awaiting the president's nomination of a permanent replacement. Trump has attacked other IGs who have issued reports unfavorable to the administration, most recently assailing Health and Human Services watchdog Christi Grimm — another acting IG — for a report on hospital preparedness for the coronavirus pandemic.

And earlier this week, Trump abruptly removed an acting inspector general, Pentagon watchdog Glenn Fine, from his role, prompting howls of protest from Democrats who said the effort was intended to chill inspectors general from making findings against the president's stewardship of his administration.

Delmar is one of two dozen members of an inspector general committee tasked with overseeing the new $2 trillion coronavirus relief law. Fine was expected to be its chairman until Trump removed him, upending the panel's progress. It's unclear who will replace Fine.

Democrats have questioned Treasury's overall handling of Neal’s request for Trump's returns and whether the White House interfered. Luttrell’s report said Treasury’s Office of General Counsel received an unsolicited letter about the issue from one of Trump’s personal attorneys, William Consovoy, but did not determine the communication was improper.

The report also noted that the office received letters from Brady and Sen. Ron Wyden, the top Democrat on the Finance Committee.

Brady said in a statement that the report “proves that earlier politically motivated accusations are debunked — Secretary Mnuchin followed the law, complied with all requests, and there is proper oversight taking place at Treasury.”

Kyle Cheney contributed to this report.