Senator Clinton responded to questions by directing the Senators to read the Actionable Review Board (ARB) reports, where they would find their answers. These reports, as well as any classified reports, are available to the Senators. It seems probable that the Senators have not familiarized themselves with the facts as they were reported or the time line of events, but have instead, in hindsight and with an incomplete understanding of the sequence of events and the incremental nature of the intelligence as it was gathered, created a fictional account of what was known and when it was known. Now they are asking questions based on this fiction.
The other possibility is that the Senators are familiar with the facts but have chosen to ignore or distort them, opting instead to present a politically motivated fictional account of the events in order to portray the administration in as negative light as possible. Simplifying and inventing a clear time line to describe what was in real time a chaotic and fragmented stream of information allows them to base their questions and criticism on the fiction they have crafted.
The clearest indication that the entire investigation has devolved into political theater rather than practical problem solving is when you see people arguing about semantics and when the President called the event a terrorist act and when he called it an act of terror. That is also when you know that they are insincere about their concern over the tragedy and are happily adopting a political posture.