Today the Senate Committee on Homeland Security and Governmental Affairs will hold a hearing with four witnesses who played a key role in securing — or failing to secure — the Capitol when it was stormed by pro-Trump protesters on January 6. Testifying will be Paul Irving, the former House Sergeant at Arms; Michael Stenger, the former Senate Sergeant at Arms; Steven Sund, the former chief of Capitol Police; and Robert Contee, the current chief of Washington DC’s Metropolitan Police Department. All but Contee lost their jobs in the aftermath of January 6.

One key question: Why were Capitol Hill authorities so unprepared for the assault? Why weren’t they ready, or at least more ready than they were?