Pyongyang’s conventional inferiority requires it to degrade the United States’ ability to sustain the attack against it. This means it essentially has no option but to use nuclear weapons first against targets such as Andersen Air Force Base in Guam…
Pyongyang can’t affect the US’ ability to respond in any meaningful way. Even if Guam sinks into the sea, there’s still South Korea, Japan, ICBs & the US Navy. On top of that, there’s no guarantee that North Korea could even hit Guam without getting intercepted, and trying but failing would certainly means a massive counterattack.
I think the big new issues with a Nuclear North Korea is probably proliferation related. North Korea has a tiny economy with exports of just 4-5bn, less than a small US city. Selling an occasional bomb could triple their exports bring in foreign currency, which they are starving for. Even if they got caught, would the US respond to a nuclear armed country?