DES is the algorithms that was secretly modified by the NSA to protect it against differential cryptanalysis. Capping a key size is hardly a "backdoor."

Also, that was the time of export ciphers and Suite A vs Suite B, which were very explicit about there being different algorithms for US NatSec vs. everything else. This time there's only CNSA 2.0, which is pure ML-KEM and ML-DSA.

So no, there is no history of the NSA pushing non-NOBUS backdoors into NatSec algorithms.