President Biden’s Justice Department is in an undeniably difficult position. Given the epic corruption of the department by his predecessor, Donald Trump, maximal transparency and accountability are now imperative. But this will inevitably clash with the department’s understandable desire to cling to certain institutional prerogatives.

Senate Democrats have a key role to play in pushing the department toward transparency and accountability. And they are doing so, prompted by the department’s highly questionable refusal to release the full memo that purportedly justified former Attorney General William P. Barr’s decision not to charge Trump with criminal obstruction of justice in the Russia scandal.

All 11 Democrats on the Senate Judiciary Committee just fired off a letter to Attorney General Merrick Garland, calling on him to release this memo in full, with no redactions. Led by Sen. Richard J. Durbin (D-Ill.), the committee chair, they argue that precedence and transparency require it.

“Please provide the memo, or your legal justification for withholding it, to the committee by June 30, 2021,” reads the letter, which was provided to me in advance of its release.

The memo is important because it could shed light on how the department — and, more broadly, the rule of law — were deeply corrupted to help Trump escape accountability for potential crimes.

After special counsel Robert S. Mueller III documented extensive potential criminal obstruction by Trump, Barr declined to prosecute. Importantly, in clearing Trump, Barr sent a letter to the Senate and House judiciary committees that badly misrepresented Mueller’s findings, while declaring that his decision not to prosecute was not driven by precedent dictating that sitting presidents are immune from prosecution.

Instead, Barr said, the decision was made on the legal merits of the case itself, citing advice by the department’s Office of Legal Counsel. That raises the prospect that Barr didn’t merely exonerate Trump; he also may have misrepresented how the legal decision was made to additionally spin him as guilt-free on the law. That’s why this memo is crucial: It could show how that really happened.

During litigation brought in response by Citizens for Responsibility and Ethics in Washington, it became clear that this memo was key to Barr’s claimed justification. This spring, a federal judge ordered the department to release it, making the extraordinary claim that the memo demonstrates that Barr did not rely on it to reach his decision.

Yet under Garland, the department continues to resist release, appealing the judge’s order, even though it could very well reveal that Barr relied on a sham justification for clearing Trump.

In their letter, the 11 Judiciary Committee Democrats spell out the real stakes of this decision.

As they note, the department is relying on the idea that Barr used this memo to inform his legal decision to justify concealing it, on the grounds that it was part of internal deliberative processes. But if Barr didn’t actually use it to reach his decision, those grounds evaporate.

If so, the Justice Department’s current leadership will be denying Congress information it needs to illuminate how the previous department leadership actively misled Congress about its perversion of the law to protect a U.S. president.

“In the interest of transparency, this OLC memo should be public – and given its role in misleading the Judiciary Committee about Special Counsel Mueller’s findings, it should be produced for the committee without delay," Durbin told me in a statement.

As the Democrats’ letter also notes, there’s plenty of precedent for the Senate Judiciary Committee to obtain such OLC memos, because they’re sometimes used to justify executive branch policies that are deeply controversial and of dubious legal grounding.

“The transparency of OLC memos remains of utmost concern to the committee given the role OLC plays in justifying executive branch policies of enormous consequence,” the letter says.

All this comes even as new evidence of Trump’s efforts to corrupt the department continues to pour forth. While it’s understandable that the department might want to protect its prerogatives, this is a truly unique situation, and the public is entitled to a full fumigation.

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