In Terminator Genesis, John Connor is the leader of human resistance and so he is aware of what the machines are doing to end with him and the human species. So he learns the latest plan they have, which is very imaginative.
The machines send one of their own to the past, 1984. At that time John Connor’s mother is pregnant with him, so the machines plan to kill the mother and thus prevent John from being born.
So they do not kill their mother in the past, John sends Kyle Reese. This is one of his most loyal sergeants, so you can rely on him for this transcendental mission. The mission is not without risks and therefore not well.
Kyle Reese is sent to the past, but not to the correct year. It remains in an indeterminate point of the past, in which the enemies of the future can now be allies, unexpected enemies, etc.