I think I have a better shot at building the Perpetual Motion Machine in my back yard than the NorKorComs have of solving nuclear fusion.
This wouldn’t be the development of a full-scale multi-stage thermonuclear weapon; it’s a slight modification to an implosion fission device (which the NORKs already have) basically putting some fusionable material in the middle of the imploding Pu or HEU to generate more neutrons and improve the fission explosion.
The trick is injection tritium into the hollow pit of a fission device just before detonation. The intense fission reaction is sufficient to start fusion of the tritium and radically increase the yield both from added fusion energy and releasing a lot more neutrons further increasing the fission yield.
Pretty sure without looking that we figured how to do this before we figured out thermonukes.