Reports that President Trump ordered the White House counsel, Donald F. McGahn II, to bring about the firing of the special counsel Robert Mueller last June are deeply troubling — not only as evidence of what the president has already done, but what he may yet do to obstruct justice and undermine the rule of law.

Whether Mr. Trump engaged in obstruction of justice is, of course, yet to be determined. But we already know the F.B.I. director James Comey said that Mr. Trump asked him to back off on the Russian election meddling inquiry, and in particular on investigating his national security adviser, Michael Flynn, and that Mr. Trump fired Mr. Comey when he refused to abide by these instructions. We have also seen reports that Mr. Trump directed Attorney General Jeff Sessions not to recuse himself from the Russia investigation, despite Mr. Sessions’s clear legal obligation to do so.

All of that, together with Mr. Trump’s involvement in a misleading public statement about the June 2016 Trump Tower meeting between close campaign advisers and Russian agents, strongly suggests that President Trump has been wrongfully trying to block the investigation.

Now there are reports that President Trump ordered the firing of Mr. Mueller last June. This is yet more evidence that the president is determined to block the investigation at all costs. It suggests Mr. Trump has something to hide about himself, his family or another associate. Therefore it goes to an element in any obstruction case, that of “corrupt intent” — whether a person’s actions were motivated by an improper purpose. An effort to fire Mr. Mueller would be particularly incriminating because it replicates the key moment when mere disgruntlement may have soured into illegality: Mr. Trump’s termination of Mr. Comey.