Then-FBI Director James Comey is sworn to testify before the Senate Judiciary Committee. (Jim Watson/Agence France-Presse via Getty Images)

PRESIDENT TRUMP on Feb. 14 asked then-FBI Director James B. Comey to drop the investigation into former national security adviser Michael Flynn’s connections to Russia, according to a memorandum Mr. Comey wrote at the time. The White House says the conversation didn’t happen as described. If it did, it would represent an extraordinarily improper effort by the president to influence an FBI investigation. The report certainly bolsters the case, already persuasive, for independent inquiries into Russia’s meddling in the U.S. election, any possible collusion by the Trump campaign — and any post-inauguration effort by the administration to disrupt investigation into any such collusion.

The New York Times, which reported the existence of the Comey memo on Tuesday, notes, “An F.B.I. agent’s contemporaneous notes are widely held up in court as credible evidence of conversations.” Mr. Trump had already admitted that he had the Russia investigation on his mind when he fired Mr. Comey last week. At the time, the investigations into Russia’s meddling and Mr. Flynn’s Russian connections were ramping up. If Mr. Trump had tried and failed to persuade Mr. Comey to discontinue the Flynn inquiry, the firing becomes all the more suspicious.

More than a generation has passed since the country so badly required an aggressive independent investigation into White House behavior. Tuesday’s news only raises more questions. How many memos did Mr. Comey write? What else may the president have improperly asked of federal law enforcement officers? The country needs to hear from Mr. Comey, see his memos and hear White House tapes of the conversations, if they exist.

The Justice Department must appoint a special prosecutor charged with determining whether any laws were broken. But that would not be sufficient. Some of the things Mr. Trump has done, such as terminating Mr. Comey, may have been legal but inappropriate. Other elements of the Russia story, such as the election hacking, may not lend themselves to criminal prosecution, as many or all of the perpetrators are outside the country. In order to provide the public a full picture of what happened inside and outside the country, Congress must empanel an independent commission. House Speaker Paul D. Ryan (R-Wis.) and Senate Majority Leader Mitch McConnell (R-Ky.) can no longer duck these issues in an effort to focus on the GOP agenda. The Russia-Comey fiasco is now the country’s agenda. Mr. Trump, if his denials are true, should welcome an independent inquiry.