Obviously, you can design a Nuke to maximize EMP
Just like building a Neutron Bomb or etc.
But your claim was:
"Merely detonating a nuke at altitude will not generate a huge EMP. To get that, one needs to design the warhead from the start to produce a massive EMP. "
I guess we can talk about what 'huge' or 'massive' is supposed to mean, but even a small fission-only nuke detonated beyond the ionosphere will induce enough of a surge in transmission lines to ruin most microcircuits plugged into the power grid (or phone system) without some sort of hardening, and quite possibly destroy even some un-plugged devices as well, like those with antennas. That would pretty much cripple a huge area of the USA. So yeah, I am concerned about Iran and an EMP weapon.
Davin L.