I've played through Dead Money, and playing throgh Old World Blues at the moment, and I'm curious why Christine was sent to assassinate Elijah. Christine states in Dead Money that "he became unstable, left a trail of crimes across the wasteland. Once word reached us, I was ordered to kill him". Her holotape in Old World Blues also states "Elijah is obsessed. He's mad. It's why they ordered his execution". But has it ever been made clear what exactly he did?
All I know is he abandoned the BoS at Helion One after the NCR attacked, and when it was clear that the BoS couldn't win, and then he turns up at the Big MT, testing bomb collars on ghouls in preparation to break into the Sierra Madre vault. I could understand if Christine was sent after him to stop him using the technology of Big MT, or to stop him having the hologram army he plans, and unleashing the Cloud onto the people of the Mojave. But she was sent before that. I can't see the BoS being concerned about the testing on ghouls and the way I understood it she was sent before he got to Big MT anyway.
So what did Elijah do? Without any other information it almost seems as if his execution was ordered as revenge for what happened to the BoS at Helios One.