Bob Bauer, the White House counsel from 2009 to 2011, is a professor at New York University Law School on leave this fall to work as a senior adviser on Joe Biden’s presidential campaign. Jack Goldsmith, a professor at Harvard Law School and a senior fellow at the Hoover Institution, was head of the Justice Department’s Office of Legal Counsel from 2003 to 2004. They co-authored the book “After Trump: Reconstructing the Presidency.”

President Trump’s four-year effort to manipulate the Justice Department to protect himself and serve his political ends has suffered some spectacular failures. The department’s investigation into possible wrongdoing related to “unmasking” has ended without incident. Trump’s frequent demands that the department indict people he considers political enemies appear unlikely to be satisfied. Trump tried to fire special counsel Robert S. Mueller III and squelch publication of Mueller’s report, but executive-branch subordinates would not cooperate.

Norms and laws worked much better in these instances than many feared they might. But Trump’s incessant norm-breaking and possible lawbreaking still damaged the appearance and reality of even-handed justice. The White House and Justice Department notably failed on several occasions to adhere to relevant norms of independence. Some deviations were significant. And a future president could follow Trump’s playbook with much greater competence.

When Trump leaves office, the damage he caused must be fixed and the possibility of future abuse urgently checked. At least six problems require attention.

1. The next administration will immediately face the fraught question of whether and how to investigate and, if warranted, prosecute possible crimes Trump committed while in office. If such an investigation of an ex-president occurs, it should take place pursuant to a transparent process supervised by the attorney general. The investigation and prosecution should be conducted by a special counsel. A former president seeking clemency should have to apply for it, and the application should not be considered until any charges have been filed. The process should include analysis by the attorney general and consultation with Congress.

2. One challenge in investigating possible presidential crimes is that it is unclear how current statutes on obstruction of justice apply to the president. As special counsel, Mueller concluded that the laws applied but noted uncertainties in application. Attorney General William P. Barr has been more skeptical but has acknowledged that a president may not, for example, alter evidence or try to persuade a witness to give false testimony. To put the strongest possible check on future presidents engaging in Trump-type machinations, Congress should amend these laws to expressly cover presidential behavior that pertains to corrupt interference in the administration of law for self-protection, protection of family or to affect an election.

3. Congress should reform the pardon power that Trump has abused (and threatens to abuse further). The Constitution confers the pardon power on the president but does not immunize this power from all regulation. Congress should amend the bribery statute to make it an independent crime for the president to bestow a pardon to try to influence testimony in an investigation. (Some have expressed concern that such a deal may have informed Trump’s commutation of Roger Stone’s sentence.) Congress should also ban presidential self-pardons, which Trump has suggested he might invoke. Such a ban would not resolve the constitutionality of self-pardons but could influence subsequent judicial analysis.

4. The special counsel regulations that governed Mueller’s investigation need reform. A special counsel is a quasi-independent investigator who examines possible wrongdoing by senior executive-branch officials. Mueller’s investigation revealed numerous problems in current regulations, including the limits on the special counsel’s authority to collect and provide Congress and the public with facts about alleged wrongdoing by a president. The regulations should acknowledge this role expressly and protect it by ensuring that special counsels can report these facts publicly even if they are fired or if the attorney general rejects their prosecution recommendation. Congress should also specify that a special counsel can be fired only for cause.

5. The Justice Department needs to amend its internal rules and guidelines to clarify that obstruction-of-justice statutes apply to improperly partisan law enforcement actions by department officials and that any such actions that fall short of obstruction of justice nonetheless violate department norms.

6. The Justice Department should reform its rules on investigations such as the one Connecticut U.S. Attorney John Durham is conducting into the investigation of the Trump 2016 campaign’s possible contacts with Russia. Such look-backs can serve legitimate purposes, but they should be conducted by the inspector general, who is more independent, rather than by a criminal prosecutor. Any criminal wrongdoing uncovered should be pursued by a special counsel rather than a prosecutor, who is more directly under the attorney general’s thumb. In addition, department regulations should specify that the attorney general is prohibited from publicly pre-judging ongoing investigations against uncharged individuals — a norm that Barr has often defied.

None of these reforms can stop a determined president from publicly commenting on ongoing investigations in ways that debase the rule of law. But as a package, these reforms could deter a president and attorney general from trying to obstruct the law enforcement process in self-serving ways. They could also reinforce the appearance of even-handed, nonpartisan law enforcement, even when the president is a determined, serial norm-breaker.

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