This post has been updated with the latest news.

It was always going to be a challenge for Republican senators to argue why they want to proceed so quickly with Judge Brett M. Kavanaugh’s nomination to the Supreme Court after he was accused of sexual assault 36 years ago. They have relied on complaints about the timing of the allegation — it was publicly reported just before they were set to vote on Kavanaugh’s nomination. But now they find themselves leaning on reasons to move forward that have some confounding logical gaps.

As Republican leaders in the Senate barrel forward with Kavanaugh’s nomination, they are doing it without having talked to all the alleged witnesses, arguing that the evidence they’ve seen shows a plausibly innocent Kavanaugh.

“There is simply no reason to deny Judge Kavanaugh a seat on the Supreme Court on the basis of evidence presented to us,” Senate Judiciary Committee Chairman Charles E. Grassley (R-Iowa) said Friday, as the committee met to debate Kavanaugh after he and his accuser, Christine Blasey Ford, testified Thursday.

The gaping hole in that argument is that there could be corroborating evidence, if Senate Republicans on the Judiciary Committee had asked for it before Thursday’s hearing. Ford places a third person in the room at the time of her attack, Kavanaugh’s high school friend Mark Judge. Judge’s presence is a key part of her story, one that struck a former sex-crimes prosecutor as elevating it to the realm of credible: “She put a third person in the room,” Linda Fairstein, former chief of the Manhattan District Attorney’s Office’s Sex Crimes Bureau, told The Washington Post. “If you were making something up, why would you do that?”

And yet Republicans did not subpoena Judge. At first they argued his statement that he can’t recall an incident like that happening was enough.

On Friday, they argued that Judge’s struggles with depression and anxiety make it difficult if not impossible to call him to be a witness.

Difficult and even insensitive to Judge, maybe. But there is a political crisis about Kavanaugh’s nomination that risks engulfing the U.S. Supreme Court, and Judge is the person who most likely could provide further evidence.

Republicans are also having to explain why they are moving to quickly confirm Kavanaugh without an FBI investigation into Ford’s claims. One of their own, Sen. Jeff Flake (R-Ariz.), called them out for it Thursday when he voted for Kavanaugh in committee but hinged his vote in the full Senate on there being an FBI investigation first. It’s not clear whether Senate Republicans will take him up on that offer.

Republicans are correct that the FBI wouldn’t definitively say who is telling the truth. But as Ford testified Thursday, it could provide important context to her story and unearth more evidence.

“I did see Mark Judge once at the Potomac Village Safeway after the time of the attack,” Ford offered early in her testimony. “And it would be helpful with anyone’s resources if — to figure out when he worked there, if people are wanting more details from me about when the attack occurred. If we could find out when he worked there, then I could provide a more detailed timeline as to when the attack occurred.”

The Post’s Philip Bump explains that she’s right. When Judge worked at the Safeway could pin down whether Kavanaugh and Judge were at a party or gathering in July with several mutual friends of Kavanaugh’s and Ford’s.

The shakiness of the logic is also compounded by the fact that Republicans are leaning heavily on supposedly exculpatory evidence from Kavanaugh that isn’t really exculpatory. Kavanaugh provided a calendar from his summer in 1982 suggesting he wasn’t at such a gathering, but it doesn’t prove he wasn’t. Kavanaugh and Republicans point to legally binding statements from potential witnesses saying that they can’t remember such a party or incident. But that doesn’t mean it didn’t happen.

None of this is to say that Judge’s testimony or an FBI investigation would back up Ford. It might prove the opposite and exonerate Kavanaugh, as Democrats repeatedly pointed out Thursday.

“If there is no truth to her charges, the FBI investigation will show that,” Sen. Richard J. Durbin (D-Ill.) said to Kavanaugh in a heated moment. “Are you afraid that they might not?”

Beyond two witnesses who give different versions of what happened that summer night in 1982, we don’t know much about the facts of this case.

But as Republicans move forward with Kavanaugh’s nomination, they are claiming they have enough evidence to determine Kavanaugh is innocent. We do know the facts don’t add up to that. At least, not yet.