Caldwell seemingly considers Hayek to be arguing little more in The Road to Serfdom than that Soviet-style command planning is wholly incompatible with a democratic polity. Indeed, taking Caldwell’s statements at face value, he would—at least when wearing his editor of Hayek’s Collected Works hat— seemingly consider Hayek’s book to have scant relevance whatsoever to contemporary debates over the welfare state and the Obama administration…. Did Hayek intend his argument in The Road to Serfdom to have exclusive applicability to a system of full-blown command planning (apparently Caldwell’s position) or also to — as Limbaugh and company would seemingly have it—have ready applicability to the mixed economy and welfare state … ?
there is much clear evidence that Hayek himself had always intended his argument to apply with equal stringency against command planning and the welfare state alike (see, e.g., Hayek 1948,  1994, 1960, and  1994). Indeed, as we shall show, Hayek—during the 1940s and after—frequently argued that the logic supposedly set into play by any policy of persisting with the mixed economy, Keynesian demand management policy, and welfare state practices would lead to full-blown central planning. Importantly, Hayek frequently claimed that the “middle of the road” policies—pretty much the welfare state and demand management (Toye 2004)—adopted by the 1945–51 Labour Government in Britain aptly illustrated the veracity of his thesis in The Road to Serfdom.
And Bruce Caldwell’s response (not paywalled):
Though Hayek had many targets in the book, the idea that socialism – state ownership of the means of production – is compatible with political freedom was certainly a chief one. … at Hayek’s dire warnings about the future take as their starting point a system of full socialism, that is, a system in which there is state ownership of the means of production … the examples of western Europe do not fit: none of them embraced a comprehensive system of planning. Perhaps needless to say, I stand by my statement … that “a welfare state is not socialism” (Caldwell, in Hayek 2007, 31). The distinction is absolutely essential if we are to understand the logic of Hayek’s argument correctly
Four years later, Hayek would offer his own vision of a new society … founded on liberal principles in his book The Constitution of Liberty. In chapter 17 of that work, in his precisely titled “The Decline of Socialism and the Rise of the Welfare State,” … Hayek asserts that the welfare state had replaced socialism as the chief enemy of liberty. He begins by noting that “socialism in the old definite sense is now dead in the western world” and that “If, fifteen years ago, doctrinaire socialism appeared as the main danger to liberty, today it would be tilting at windmills to direct one’s argument against it” (Hayek 1960, 254). But what had taken its place, enthusiasm for “the welfare state,” was in many ways more dangerous. Hayek notes that, “unlike socialism, the conception of the welfare state has no precise meaning” (ibid., 257). It has no distinctive principles, other than some amorphous desire to increase social justice. But this makes the task of fighting against it much more difficult … Hayek paints a portrait in which, slowly and over time, the accretion of interventions in the economy gradually and unintentionally lead us to the kind of centrally planned system that all now rightly regard as something to avoid.
And these are indeed the sort of slippery slope arguments that F&M want to associate Hayek with in the [sic] The Road to Serfdom. … In his later work, the slow but steady growth of the welfare state appears from the outside as much more benign, and precisely because of that, from Hayek’s perspective, is much more insidious. No jackboots or gulags accompany the growing power of the welfare state – at least not until later. Rather, the death of liberty is that of a thousand small cuts, each aiming at correcting some apparent flaw in the system. This is a very different argument from the one in The Road to Serfdom, and one should not mix them together.
In short, Bruce Caldwell’s defense is not that Hayek didn’t claim that the welfare state was the slippery slope to gulags and jackboots – it’s that he didn’t say this in The Road to Serfdom, although he did say it in his later works, and that one shouldn’t mix up the two arguments. Although Caldwell doesn’t mention it, Hayek himself conflates these arguments in his own introduction to the US edition of The Road to Serfdom, which was written after he began to worry more about the welfare state. Finally, Judt doesn’t actually attribute this argument of Hayek to The Road to Serfdom in any of its editions; he is talking, more generically, about Hayek’s “writings.” So I’m calling this one unequivocally in favor of Judt – contra Tyler Cowen, he wasn’t being unfair at all. And if Greg Ransom wants to argue in comments that notorious left-wing provocateur Bruce Caldwell is ignorant and dishonest about what Hayek says, he’s free to make the best case he can, (as long as he supports his tendentious accusations this time with facts, references etc).