President Donald Trump has repeatedly threatened to take drastic action to undermine special counsel Robert Mueller’s investigation into the Trump campaign and Russian interference in the 2016 election. His latest target is Deputy Attorney General Rod Rosenstein, who oversees Mueller.

If Trump seeks to undermine the investigation and obstruct justice by firing Rosenstein, there would be serious concerns about the impartiality of any political official at the U.S. Department of Justice who replaces him. These concerns are heightened by Trump’s repeated demands that the Department of Justice protect him from accountability for his actions. The only way to repair the trust of the American people in the integrity of the investigation would be to follow past precedent and ensure the special counsel is truly independent.

Just as the Nixon administration did, the acting attorney general for purposes of Mueller’s investigation must enter into a written delegation agreement that provides full authority to the special counsel.