Kant is a tricky topic because while the majority interpretation of him is as an Idealist (pretty much as Rand outlined, main modern representative being Paul Guyer), there’s also a minority interpretation that takes his 7 or so disavowals of Idealism seriously, and stresses the “Empirical Realist” side of him (main representative Henry Allinson, with I think the best explication being by a chap called Arthur W. Collins, who goes a bit further than Allinson in a fascinating little book called Possible Experience).
So much depends on which Kant you’re talking about, and when it comes to the baneful influence of Kant, that might actually be more like the baneful influence of a tragic misunderstanding of Kant.
Not that he’s completely innocent even on this reading - he certainly did want to “make room for faith” in some sense, but certainly not in the realm of ordinary, everyday experience (which is where Objectivism lives too). He was also a fan of Rousseau, and there are definitely elements of collectivism and altruism, etc., in his thought. However, as he states plainly, where he wants to “deny reason” is in being competent to discuss God, the immortality of the soul, etc., and that’s the only extent to which he’s “Idealist”, i.e he’s “idealist” about matters that don’t touch on empirical reality anyway.
The key to the alternate reading of Kant’s epistemology is to understand what the “dogmatic slumbers” he felt Hume had awakened him from were. Bear in mind the historical context: he was a rationalist in the tradition from Descartes to Leibniz, but shared the starting point of Cartesianism with the British Empiricists, the starting point of methodological solipsism and _representationalism. _If you read Kant as someone trying to step outside that starting point, and you take “Empirical Realism” seriously, then you start to understand Kant as a revolt against Cartesianism in a sense roughly parallel to Thomas Reid, with Kant’s innate categories being roughly parallel to Reid’s Common Sense. (It’s interesting that Kant only knew of the Scottish school via Beattie, who he despised - it would be interesting to see what his reaction to Reid himself might have been.)
And both of those as roughly parallel to Objectivism. Obviously not in detail and jargon and working-out, but in the sense that these three philosophies are closer to each other than any of them are to either rationalism as such, or empiricism as such. All three are stepping outside the Cartesian starting point that makes the rationalist/empiricist division seem compelling, and stepping back into a kind of - well, Empirical Realism.
The trouble is, while Kant was revolting against the Cartesian tradition, he was using jargon terms derived from a mixture of that and the older scholastic tradition. And this is why you can have a sort of “double vision” while reading Kant. At times it really, really seems like he’s an Idealist, particularly when he uses words like “Vorstelling” (representation). But if you calmly recall to mind his disavowal of Idealism, then you can start to see how for him, the vorstellung is more like the “form of appearance” of Rand, which is more or less like the “sign” of Reid. Also, there’s the factor that it’s just a really difficult problematic he was working with, so he did get confused himself sometimes.
As to the famous thing-in-itself, of course if you understand Kant in Cartesian terms, then it’s all as Rand says, you have this sharp disjunct between representations being the things we perceive and experience, on the one hand, and a world “behind” that “flat plane” of representations that may or may not correspond to it. But if you take Kant in Direct Realist terms, or as he called it himself, Empirical Realist terms, then there is no such sharp cut. The thing in itself is precisely the thing we experience. “Experience” isn’t used in a way that latches onto the internal representation, but rather onto the object out there that’s independent of the mind. The thing-in-itself and thing-of-experience distinction is then purely epistemological, it’s purely a way of conceiving things. Which is why Kant never saw the obvious howler that so many think they see: that the proposal that causality can come from the in-itself and cause phenomenal experience is unjustified. It would be unjustified if the distinction between thing-in-itself and thing-experienced were metaphysical. But for Kant - the real Kant - it’s actually not.
Something that adds to the confusion here is the notion of the noumenon. Most commentators have elided the distinction between noumenon and thing-in-itself - THEY ARE NOT SYNONYMOUS. The concept “noumenon” already contains within itself a proposal as to means of verification, i.e. the noumenon is the thing-in-itself considered as susceptible to being understood by a God-like intuition, i.e. precisely a kind of mystical perception, as Rand would have understood it. That is all Kant denies about the thing-in-itself - that we can intuit the thing-in-itself by means of such a God-like awareness.
Anyway, the upshot of it is that for the real Kant (in this view) we are not in any way metaphysically cut off from things, the thing-in-itself and the thing-of-experience are one and the same thing, simply conceived in different ways. And what Kant is saying is that we have no way of conceiving of things that isn’t in terms of possible experience, in terms derived from possible experience, or in terms of what makes experience possible: but that’s not a problem.
A simple way of putting this would be to consider thinking of a presently-unexperienced object. Is it coloured “outside of experience”? It depends on how one thinks of colour, as the phenomenon that occurs when the surface reflectivity of objects interacts with our sensory/perceptual system, or as that surface reflectivity as a property of the object alone. However, even though we can understand the surface reflectivity as the property of the object that’s there independently of our experiencing it, we can think of it (e.g. picture it) only in terms of being coloured in the former sense, as notionally giving off, outside our experience, that interactive causal effect its surface reflectivity has on us while we experience it.
And that’s actually ok. It’s simply conceiving of the object as an object of possible experience. This admits of an active conscious aspect to the process, but it doesn’t deny the metaphysical independence of the object from consciousness, it just denies that that metaphysical independence can have “its own way of being spoken about”, a way that’s not in terms derived from possible experience.