Also, the US can't enforce "legally mandated backdoors" on every foreign made phone. It seems somewhat unrealistic to me to tell every visiting businessman or tourist that they can't bring a phone into the US. I suppose it would be possible to go the UK route and make use of encryption a criminal offense for US citizens, but that's a bit of an uphill battle that won't hurt criminals much.

The pound is defined as (exactly) 0.45359237 kilograms. If the kilograms gets lighter, the pound gets lighter. If the kilogram gets heavier, the pound gets heavier.

I compiled a new kernel. It was in the old dark days of Linux 1.2 and the module system didn't yet exist, so you had to recompile the kernel to get support for your hardware.