My initial instinct on Depp was INFJ from the start. NFs tend to emit a certain kind of warmth that I do not experience with other types (just as NTs express a certain kind of clarity but but "coolness" -- impersonality -- at some level). He also seems to lock into his roles with the certainty of a J, where P's tend to "play around with the roles" more -- and he's more enigmatic about his personal life and truly matters (tends to happen because there's a wealth under there with the Ni, but the outward expression is dominated by Fe patterns), whereas INFP exposes Ne when it interrelates and tends to be more open about itself and its thoughts, expressed through ideas.
I still think Clinton is an ESFP (he's akin to the ESFPs I know personally, and NOT akin to the ENFPs I know); but I'm tired of discussing him for the 30x time, so you can make whatever decision you'd like.
I think one flaw in trying to determine a personality by determining 'strongest function' is that we can't see clearly inside, and as people age (as Meshou pointed out), weaker functions hopefully become more developed, masking the instinctual/preferred functions.
I tend to use some of that, plus a mental "personality snapshot" that accumulates pictures of what each type generally "looks like" in real life, and then I use look-and-feel to help me make a good opening guess, which I can then hone in on. One flaw in this approach is, of course, is accumulating a full range of snapshots to begin with... so if you haven't been exposed to a particular manifestation of a type and have it in your database, you won't find a match or you might match things up elsewhere. (Such as with my initial difficulty in thinking about Ivanka Trump, who likely could be ESTJ despite not matching up to the more typical sorts I've encountered.)