In short: it's not Facebook's or WhatsApp's fault, but they're forced to cheat if there is the requirement from US officials.
While there may be E2E encryption in WhatsApp, there is no way to get it trustworthy.
Of course the government will try to threaten them with NSLs or tax audits or whatever, and Whatsapp could cave, but the law should be on their side.
But before we get there they actually have to put it in their privacy policy that they are doing that, so then they can show the judge later that they've legally committed to a certain level of privacy for their users.
they just pay them to include the additional primes in the public key system. users are still more or less secure. not just whatsapp. pretty much all the public key systems use it. it's still effectively 1024 bit plus keys for everyone but the nsa and ghcq.
latest snowdon leaks include everything you need for confirmation now you know what to look for.
this gives them the key used for the encryption and allows them to decrypt the messages. but still makes it hard for everyone else to decrypt (since they don't know the nsa primes).
no I'm not going to share the keys they use.