For the one that says, "I am leaning your way:" If you are going up against a human, you don't need to add anything until he starts leaning towards the other human team. If you are going up against a SIM, you need to keep spending until you are the only one he is considering.
If you aren't the one in the lead (against a human), and you want him, you need to spend more until you are in the lead.
SIMs have to be knocked off the considering list in order to sign the recruit.
Against a human, as long as you are in the lead, you'll get to sign the recruit eventually.