He basically wants the right to secretly dig a tunnel under your home, sneak in while you're not there, steal whatever they want, and leave without anyone knowing it. Except in your phone.
Even worse: he want the tunnels being pre-dug (= "backdoors").
You know how in Switzerland every house has a mandatory under-ground shelter ?
What he wants is every single house in the USA having a mandatory underground tunnel that leads to a nearby police station. A *secret* tunnel that you're forbidden to know about when you buy your house.
That's what an encryption backdoor is the equivalent of : a mandatory secret back-door built in every house in the USA.
And with the automation and international connection that is available on the internet, the real-world situation is even worse than this putative mandatory tunnel.
(Now the metaphor is getting a bit harder...)
It would be as if the police station had an nearly infinite amount of low-ranking police personal that could devote their entire time to travel the tunnel each day, sneak into your house every single day, and take a picture of you naked in your shower. And not only you personnally, but though every tunnel, available in every single home built on US soil under US building code. Each fucking day.
But said local police station lacks trained and experienced detective to do anything useful out of the photos/objects/proofs brought back from by the agents.
And meanwhile, all the people living outside of the USA are completely immune to it because their local building code either don't mandate the tunnel (and thus, the US police agents can't even use this tunnel network to peak into the homes of ISIS terrorists, although that was the main selling point of the tunnel network when it was voted in)
Or mandate an entirely different type of tunnel that the US police has never heard off (and leaves some part of the US population at risk, because they buy and install a port-a-potty from China, and never realise that these come with tunnels leading directly into their chinese secret police).
All the while the Russia mafia has trained an incredibly huge army of burglars to roam the US (and Chinese) networks of secret tunnels, stealing as much as possible from every house they happen to reach. And even sometimes using your own house as a base of operation to commit crimes while you're away for work. (botnets).
At the end of the operation, maybe 1 single terrorist happens to get caught due to random chance. And maybe due to the fact that he was bragging that he is a terrorist the whole day in the middle of the street ( = wasn't even using encryption at all. Just plain text SMS.)
At the same time there will be millions of damage due to stolen property through the tunnels network.
( = just have a look at the massive data leaks that you have *today* when hacker still go through the long round about route of actually hacking into servers. Now think how much more damage would be done when the hack don't actually even bother to hack, but just leverage the backdoors that are mandated by the various governments)