PRESIDENT TRUMP insists he wants the FBI to conduct “a very comprehensive investigation” into sexual misconduct allegations against Supreme Court nominee Brett M. Kavanaugh. “I want them to interview whoever they deem appropriate, at their discretion,” he tweeted Saturday. “The person who is going to take that position is going to be there for a long time. I have a very open mind,” he elaborated at a Monday news conference.

Yet reports suggest that the administration, or Senate Republicans, or both, are trying to limit the probe unreasonably. The Post’s Mike DeBonis and Josh Dawsey reported Sunday that the FBI will interview only Mr. Kavanaugh, two of his three accusers and people alleged to have been at the two incidents in question. The FBI thus far apparently has failed to approach a third accuser, Julie Swetnick, whose allegations are the most extreme. White House counsel Donald McGahn is reportedly the administration official most involved in shaping the inquiry.

“There are multiple allegations currently in front of the committee, and I think it is not hard to figure out the universe of witnesses,” said Christopher A. Coons (D-Del.), one of the senators who brokered a last-minute deal that led to the FBI investigation. “It is not 500. It may not be 50. But it has to be more than five.”

You’d think Mr. Kavanaugh and his supporters would want the FBI to look into the Swetnick allegations, given the judge’s assurances that those charges are total fabrications. Agents also should talk to other participants in Mr. Kavanaugh’s social circle in high school and college, starting with those who appear regularly in his calendars, to determine the truthfulness of his statements, under oath, to the Senate Judiciary Committee — about his drinking, for example. Another of his Yale classmates just said publicly that Mr. Kavanaugh’s partying was far more excessive than he let on. And are his relatively innocent explanations for the innuendo on his high school yearbook page plausible? Given the absolute discrepancy between his testimony and that of Christine Blasey Ford, Mr. Kavanaugh’s credibility must be tested.

Investigators should also scour Ms. Ford’s account. Interviewing a wide number of people might help them determine, for example, who might have driven her to and from the party at which she claims Mr. Kavanaugh assaulted her — or find little corroboration. Ms. Ford in her testimony offered new clues that might pin down the timing of the alleged assault; those details, too, must be checked.

Mr. Trump said Monday that a thorough FBI investigation would be “a good thing for Judge Kavanaugh.” Given Mr. Kavanaugh’s protestations of innocence, he ought to agree. “We certainly want the FBI to do a real investigation,” Sen. Jeff Flake (R-Ariz.) said Monday. “It does no good to have an investigation that just gives us more cover.”

Mr. Flake and a handful of swing Republicans should not be the only ones to make that point. Senate Majority Leader Mitch McConnell (R-Ky.) did not inspire confidence Monday when he carped about “endless delay and obstruction” and vowed a vote this week, apparently without regard to the status of the FBI investigation. For the good of the court and the nation, he should be pressing, as should Mr. McGahn and Senate Judiciary Committee Chairman Charles E. Grassley (R-Iowa) for the “comprehensive” investigation that Mr. Trump has promised.

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