The protocol itself would still seem to be safe (or rather, have safe combinations of key exchange and encryption).
But it is certainly feasible that if they manage to find cracks in popular-but-old communications protocols that they are able to automatically decrypt them, or use prior key recovery successes to bootstrap fast attacks on new communications from the same host.
What would be interesting is if NSA's own "Suite B" crypto recommendations are susceptible to these risks, as that would potentially represent a rather significant break in the U.S.'s own COMSEC, and COMSEC is one of the things NSA is very specifically tasked with ensuring are safe with no backdoors for anyone to jump through.
Backdoors in the NSA recommendations could be due to trapdoor functions that only NSA has the key for. Other parties would therefore be unable to utilize that backdoor (short of the secret being exfiltrated).
Inserting such a keyed backdoor is much more difficult to do undetected, and more limited in scope (has to be done separately for every crypto algorithm being backdoored), than introducing a flaw in a hardware or software RNG implementation.
But it is certainly feasible that if they manage to find cracks in popular-but-old communications protocols that they are able to automatically decrypt them, or use prior key recovery successes to bootstrap fast attacks on new communications from the same host.
What would be interesting is if NSA's own "Suite B" crypto recommendations are susceptible to these risks, as that would potentially represent a rather significant break in the U.S.'s own COMSEC, and COMSEC is one of the things NSA is very specifically tasked with ensuring are safe with no backdoors for anyone to jump through.