In keeping with her longer essay on Mario Tronti and Weber, Sara Farris has done an interesting comparison between Tronti and Althusser in her contribution to the book Encountering Althusser. There is no point to recreating her discussion of Tronti, as it is a shortened and re-focused version of the article from Historical Materialism 19.3. What is interesting is her discussion of Althusser and the state, especially since it is the late Althusser who is normally credited as being more radical rather than his earlier self.
The focus is the essay 'Marx in His Limits', in which Althusser was attempting to cope with the crisis of Eurocommunism and the failure for the PCF of the 'Union of the Left' and the Common Program in the 1978 elections. What is ultimately interesting in this essay is how utterly confused it is, as a work that does not take one step away from the Orthodox Marxism of the day, but retreats from the claims of Althusser in the 1960's that would lead to the Eurocommunist apologetics of Poulantzas and Balibar around the state.
Althusser holds closely to the idea of the state as a machine, albeit a special one. Thus the reification of the state as a thing is the starting point of Althusser's conception, taken wholesale form Lenin.
Further, the state is an apparatus because it must remain separate from the class struggle in order to intervene, but it is nonetheless the state of the dominant class insofar as it always protects the interests of the dominant class against its own follies even.
The strictly functionalist presentation of the state by Althusser should be the first warning that this is as much of a sociological, and thus uncritical, analysis as anything Weber ever did. More importantly, the state is not presented as a form, a mode of existence, of the capital-labor relation because that is understood as something economistic. This is because social form is always understood in a reified manner by Althusser. The movement to class struggle in this case is not about the primacy of the dynamic of the capital-labor relation in constituting other social forms, but about the relation of an instrument to a constituted class, as if the capitalist class and not Capital was the subject of capitalist society. The abstract nature of domination is not grasped, and instead Althusser works with a model from Orthodox Marxism, of a direct, and personal relation of domination constituted by a class and its members and their instruments.
This is the very opposite of Marx's conception of social form. And insofar as Althusser cannot grasp social form and its constitution, as well as its historical specificity as an abstract, indirect form of domination, he cannot grasp the state. Thus his call for a return to the masses comes in the midst of generalized defeat. It is a call into the void for a return to a moment that is behind. Thus Althusser was championing the party against the masses in 1968 and the masses against the party in 1978. In both cases, in both moments, he manages to be in exactly the wrong place, at the wrong time. In neither case does he introduce anything theoretically novel except for the appropriation of the latest bourgeois sociology. On this point, and quite possibly only on this point, is there a real difference between Tronti and Althusser, that they opt for different sides of the neo-Kantian divide in their theoretical poverty and political decline.