While watching the Godfather I heard this:
Sonny was hot for my deal, wasn't he? And you knew it was the right thing to do...you gotta talk some sense into him. The Tattaglia family is behind me with all their people. The other New York families will go along with anything that will prevent a full-scale war. Let's face it, Tom, and all due respect. The Don, rest in peace, was slippin'. Ten years ago could I have gotten to him?
I'm not clear why they used the past Pr. here. As far as I got,'slip' means to get less or worse in level or quality. So to me, the sentence doesn't make much sense. Maybe you can give a little explanation?