It’s getting harder and harder for him recently to come up with conventional explications. I think the biggest problem will be when data from multiple systems is declassified as it will really challenge various debunking theories.
It most probably is just a failure of imagination.
Of course, no amount of data will put this to rest. When other instruments will have failed to register the same event, people will not accept the obvious conclusion (the one instrument that "caught" it was malfunctioning/misinterpreted one way or another), they will start claiming that not only are the objects special, they are also invisible to radar/infrared/[...].
Furthermore, even if it is absolutely true that the military has a huge host of UAP that they have worked hard to identify and failed, and they are briefing the senators on the details, that does not mean that there is no explanation, it just means that trying to accurately explain a phenomenon that happened once or twice is extremely hard.
I have a backlog of dozens of bugs in my product that a customer has seen once or twice, with logs that show me they are right, that make no sense given the code and that we have been unable to reproduce. Should I conclude that alien devices interfered with my software to deceive my customer? Obviously not: complex systems are complex and have many corner case behaviors that we may never have a completely satisfying explanation for.