state university as police are still trying to piece together the gunman s motive. this hour, i ll ask the michigan attorney general about the many unanswered questions in this investigation. also today, former vice president mike pence is speaking out for the first time about his plans to fight a new subpoena from the u.s. justice department. he s arguing that his effort to avoid testifying in the special counsel probe of donald trump is about the separation of powers. republican nike y haley kic off her 2024 presidential campaign. she says it s time for new leadership, taking veils swiped at former president trump. welcome to our viewers in the united states and around the world. i m wolf blitzer. you re in the situation room. we begin with tonight s vigil for the victims of the michigan state university mass shooting. the pain and grief still very raw two days after the attack. miguel marquez is on the scene for us there. miguel, tell us more about this vigil and t
thank you, madame chair, for the question. reporter: one focus, the system that failed last month, triggering the first ground stop since 9/11. the cause, a contractor accidently deleting files during system maintenance. that no longer have access to the facilities. reporter: the faa is moving to a more modernized system by 2025, and is putting safeguards in to prevent a repeat. we re about halfway through it. is there a redundancy being built into it, or can a single screw up ground air traffic nationwide? we do have redundancy. can i say there will be another issue? no, i can t. but we are making every effort to modernize and look at our procedures. reporter: but now, aviation safety is under the microscope, after two near collisions at jfk