There’s no trap here. The Democrats deliberately waited until after Kavanaugh testified before releasing this allegation, so he doesn’t even have to answer any questions about it at all.
Or they waited until the hearings were over so he couldn’t respond. Or they waited because they are juts trying to drag it out. Or they waited so they get him to try to make statements they could then try to disprove. He was smart to keep the denial as brief as it was. If he had said he didn’t know her, or there was no party, he’d be in trouble if the Dems get the other two boys to come forward.