You know, I just discovered a plot hole in RE4...
After Leon finds Ashley, Saddler decides to tell them both about his plan, the plan is to infect Ashley and return her to her father in order to influence the United States.
He knows Leon came to rescue her, so why doesn't he just call off his forces and let Leon take Ashley to the estraction point?
Neither of them know that they are infected and Ashley is only reminded that she is infected after Saddler starts explaining his plan.
If he just kept his mouth shut he his plan would have been a success and he would get a 90s movie action hero as an ally!
I guess you could make the argument that they would find Luis along the way who would tell them both that they are carring Las Plagas inside their bodies (Maybe even Ada since she helped Luis), but even then I think there's some flawed logic in there, and it just makes Saddler look like an idiot.