Under the assumption that pseudorandom functions exist with "exponential hardness" as specified in their main theorem, Razborov and Rudich show that these proofs cannot separate certain complexity classes.
Notably, assuming pseudorandom functions exist, these proofs cannot separate the complexity classes P and NP.
Roughly speaking, the constructivity condition requires that a property be decidable in (quasi-)polynomial time when the 2n-sized truth table of an n-input boolean function is given as input, asymptotically as n increases.
There is strong current belief that the mechanism of this paper actually blocks lower-bound proofs against the complexity class TC0 of constant-depth, polynomial-sized threshold circuits, which is believed but not proven smaller than P/poly.
[4] However, some researchers believe that the Razborov-Rudich limitations are actually good guidance for what a "super-natural" lower-bound proof might involve, such as properties hard or complete for exponential space.