ταῦτά τις σαφῶς ἐπεγνωκὼς χρόνοις μὲν ἴσως διαμαρτήσεται λέγων ὑπὲρ τοῦ μέλλοντος περὶ πολιτείας, τὸ δὲ ποῦ τῆς αὐξήσεως ἕκαστόν ἐστιν ἢ τῆς φθορᾶς ἢ ποῦ μεταστήσεται σπανίως ἂν διασφάλλοιτο, χωρὶς ὀργῆς ἢ φθόνου ποιούμενος τὴν ἀπόφασιν.
Anyone who clearly perceives this may indeed in speaking of the future of any state be wrong in his estimate of the time the process will take, but if his judgement is not tainted by animosity or jealousy, he will very seldom be mistaken as to the stage of growth or decline it has reached, and as to the form into which it will change.
I'm interested in the bolded part. I understand the meaning, but I don't get the syntax. The main verb is διασφάλλοιτο which according to LSJ in the Pass. means "fail of" and takes a gen. But what are we to make of the τὸ and the ποῦ and the ἐστιν? I thought maybe τὸ ποῦ might mean something, but LSJ comes up empty. Any ideas how this works or if some words are implicit?
Thanks in advance.