Too Late
"We assume by "voluntary cooperation," the President is willing to be told to get lost by the tech giants in November – if they have the strength to do so."
That's over. Google and Apple, and I expect other companies, have already proven their strength to 'Just Say No' when the government demands the impossible, decrypting the encrypted without the keys to do so.
Then add in the fact that anyone can access and use publicly available unbreakable encryption for their files. Unless those encrypted files have a worthless password or someone discovers the keys, they're staying encrypted.
Meanwhile, no doubt the government will continue to use and create new methods of intercepting information before its encrypted or after it's decrypted by an intended receiver.
Let's just hope the US government figures out that they are required to abide by The Fourth Amendment to the US Constitution whether they like it or not. Any evidence collected outside of the mandates of the Fourth Amendment will be judged worthless and thrown out of court, as is currently being proven daily. IOW: Follow the law or your case is sunk. No '1984' scenario is welcome here. Deal with it.