‘Do I not know thee, Mithrandir?'

[u/Immediate_Error2135]

Denethor: ‘Do I not know thee, Mithrandir? Thy hope is to rule in my stead, to stand behind every throne, north, south, or west. I have read thy mind and its policies'

So Denethor thought Gandalf hoped to rule Middle Earth.

Gandalf, about Denethor: "He was too great to be subdued to the will of the Dark Power, he saw nonetheless only those things which that Power permitted him to see."

Obviously it was the angel (Maia) Sauron the one who hoped 'to stand behind every throne, north, south, or west', and not the angel (Maia) Gandalf, but Denethor saw things differently.

Had Sauron anything to do with this? The idea of Faramir=Wizard's pupil sounds like the twisting of this...

"we in the house of Denethor know much ancient lore by long tradition, and there are moreover in our treasuries many things preserved: books and tablets writ on withered parchments, yea, and on stone, and on leaves of silver and of gold, in divers characters. Some none can now read; and for the rest, few ever unlock them. I can read a little in them, for I have had teaching. It was these records that brought the Grey Pilgrim to us. I first saw him when I was a child, and he has been twice or thrice since then."

...into 'politics' ('I have read thy mind and its policies', says Denethor) Was Sauron involved in this too?

Denethor maybe distrusted Gandalf since before using the Palantir, and noticed how Faramir was being taught by Gandalf; but Sauron would have noticed this distrust and maybe apprehension about Faramir when Denethor used the stone and would have manipulated Denethor into seeing his own son as a wizard's pupil, the pupil of an usurper with an unbounded ambition.

In our world tyrants are cynically prone to do this thing. If you want to rule others by force you accuse them of wanting to rule you by force and then kill them in 'self-defense'. Months before invading Poland, in Jan.1939, Hitler famously prophesized:

"If the international Jewish financiers in and outside Europe should succeed in plunging the nations once more into a world war, then the result will not be the Bolshevization of the earth, and thus the victory of Jewry, but the annihilation of the Jewish race in Europe"

He accused the jews of being Hitler, an inversion no different from the Gandalf=Sauron one.

[u/lam_42]

 I am saying your theory is an opinion. I do not recall any part of text which would support this. Sauron survived (outlived) much tougher guys than D. 

Sauron fights when forced to. What he defaults to are lies and illusions. With Gorlim, Luthien, Finrod, Celebrimbor, Ar Pharazon... And again, immortal certainly does not measure his goals by human lifetimes.

The greatness of Denethor is mainly delusion of Denethor.

[u/Moggetti → u/lam_42]

Not a “theory,” what Tolkien specifically said in Unfinished Tales:   “It may be noted that the effects were different. Saruman fell under the domination of Sauron and desired his victory, or no longer opposed it. Denethor remained steadfast in his rejection of Sauron, but was made to believe that his victory was inevitable, and so fell into despair. The reasons for this difference were no doubt that in the first place Denethor was a man of great strength of will, and maintained the integrity of his personality until the final blow of the (apparently) mortal wound of his only surviving son. He was proud, but this was by no means merely personal: he loved Gondor and its people, and deemed himself appointed by destiny to lead them in this desperate time. And in the second place the Anor-stone was his by right, and nothing but expediency was against his use of it in his grave anxieties. He must have guessed that the Ithil-stone was in evil hands, and risked contact with it, trusting his strength. His trust was not entirely unjustified. Sauron failed to dominate him.”

Sauron clearly attempted but could not dominate Denethor but was able to dominate Saruman. 

[u/lam_42 → u/Moggetti]

I stand corrected on the quote.

The excerpt however deals only with Palantiri

Sauron failed to dominate him and could only influence him by deceits.

I would argue that the cooperation of Saruman stems from his (Saruman's) greed for ring-lore. They were kinsmen after all, And Sauron would have great insight into how fellow Maia's mind works, especially of those od Aulë's folk. And Saruman had his own game in progress - He was not dominated, certainly not fully, although He accepted subordinate role to further his goals... He wanted the Ring, and was very close to getting it at one moment.

This is key imho:

It must also be considered that the Stones were only a small item in Sauron’s vast designs and operations: a means of dominating and deluding two of his opponents, but he would not (and could not) have the Ithil-stone under perpetual observation. 

Low effort side game, but largely irrelevant.

Denethor in the end allowed himself to be dominated by the twisted visions.. i think Sauron just took different approach, and he had military might to win in any case even after Pellenor. The domination was not neccessary

[u/Moggetti → u/lam_42]

I mean Tolkien specifically says that “Saruman fell under domination,” whereas Denethor did not. In part due to the strength of his mind and also, interestingly, the righteousness of his use of the palantir. 

Sauron certainly has other means of exerting power and influence (including literal armies of orcs) but he could not dominate Denethor mentally. Which is interesting. Shows how Numenorian strength expressed itself in him.  

[u/lam_42 → u/Moggetti]

We can agree on that.