Denethor, Aragorn and Gandalf
was a thread that touched on some of this.
One point made was that Denethor had quite a few reasons to be concerned re: G and Aragorn. Some tainted w/ pride others merely prudent.
1] Aragorn's forebearers had let their kingdom dissolve, even with major Gondorian and Elvish intervention. Why trust a line whose Kings had lost firsr a kingdom[arnor] then a 'princedom' [arthedain]?
2] Just how honest was Gandalf w/ Denethor as to who he was and what his commision was, he hints at it with the ' do you not know I am also a steward' but perhaps plainer speech was in order.
3] Did Aragorn perhaps aid in Denethors suicide by failing to sail into the Harbor at Pellenor w/ a Gondorian Banner instead of the White Tree?
Surely he would have thought out that D. and many others would spy their arrival.
4] Denethor may well been aware of the activities of the White Council and been bitter about non-inclusion. He may well have fronted the largest of the armies [excepting rohan] and certainly was holding a line [more or less] that gave the 'Wizards, Elves and half-Elves' a much greater freedom to shore up their defences and plan strategy.
5] Gandalf's 'brother' wizard had just gone renegade, why should he trust Gandalf?
6] Why no serious allies offering help from the North, just a throne claiment and a few hobbits and one each of an Elf, dwarf and a Wizard.
7] Denethor may well have suspected or even seen [unlikely given the nature and tone of his questioning of pippin] Boromir die [hearing the horn and running to the Palantir]. But he could undoubtedly only have been suspicious that as soon as they were within the Bounds of Gondor, B. is dead fighting many orcs alone of the company!
8] Gandalf was hardly playing straight w/ D. re: Aragorn and his immediate plans. He may well have guessed that the Palantir had been recovered and instead of being handed to him, Gandalf acted unilateraly and gave it to Aragorn.
While all of the above was seen [if D knew it all which is unlikely] from D.'s paranoid and proud mind, it seems G did little to assuage D's fears, and indeed w/ his stance to Aragorn fixed, it would be hard for him too.
Yet nonetheless in hindsight I can't help wonder if D. could have been treated more along the lines of 'Council Members'.