The Comey memo provides the most direct evidence of Trump attempting to interfere in the FBI’s work investigating the president, his associates, and whether they colluded with Russia to influence the 2016 presidential election.

The White House disputed the memo’s accuracy in a statement:

While the President has repeatedly expressed his view that General Flynn is a decent man who served and protected our country, the President has never asked Mr. Comey or anyone else to end any investigation, including any investigation involving General Flynn. The President has the utmost respect for our law enforcement agencies, and all investigations. This is not a truthful or accurate portrayal of the conversation between the President and Mr. Comey.

Trump also denied in his NBC News interview that he had ever asked Comey to drop an investigation. But as the Times writes, “An F.B.I. agent’s contemporaneous notes are widely held up in court as credible evidence of conversations.”

The disagreement represents the most direct conflict so far between Comey and the administration. In this case, the White House is calling the former FBI director, who has a reputation for honesty even among his detractors, a liar, and staking its own credibility against him—a credibility undermined by its constantly changing justification for his firing. This follows a bizarre tweet from Trump last week, in which he appeared to threaten Comey, saying he had “better hope that there are no ‘tapes.’” The administration has refused to say whether or not tapes of White House meetings exist. If they do, they would be public records and subject to subpoena. For the time being, Comey’s memo may be the most reliable record of any conversations.

That’s probably not an accident. Comey is known for keeping records of his conversations in order to create a paper trail in the event of a disagreement. In this case, as well as in the case of another story last week that reported on a dinner at the White House where Comey reportedly said Trump asked him to pledge personal loyalty, the fired director appears to have laid a series of booby traps for Trump ahead of his firing, ensuring that his side of the story would be told—even as Comey himself remains silent.

During a Senate hearing last week, FBI Acting Director Andrew McCabe stated that the administration had not attempted to interfere with the Russia investigation, but Comey’s memo suggests otherwise—as, perhaps, does his firing. The memo, if confirmed, will elicit accusations of political tampering and perhaps even obstruction of justice by the president. Obstruction of justice was one count against President Bill Clinton in his 1998 impeachment.

Comey’s firing drew disapprobation from both Democrats and Republicans, and congressional investigators have sought to have Comey testify, though he does not appear to have agreed to any specific appearance so far.