From a piece linked at AT:
the notion that we don’t have to worry about North Korean nuclear missiles because they cannot “miniaturize” warheads is a myth. Adm. William Gortney, Commander of North American Aerospace Defense Command (NORAD) is correct to presume that is the case and to prepare to defend against that threat, as he said last October. Technologically, “miniaturizing” a nuclear warhead is much easier than developing an atomic bomb or a multi-stage missile for orbiting satellites — as North Korea has already done. Ever since the USSR orbited Sputnik in 1957, analysts have rightly credited any nation that has tested nuclear weapons and orbited satellites with the capability to make a nuclear missile warhead.
Miniaturization was no huge obstacle to the United States. According to the “Nuclear Weapon Archive” just a few years after destroying Hiroshima with an A-Bomb weighing 9,700 pounds, the U.S. Army had the T-1, a man-carried atomic landmine weighing 150 pounds.
A major problem with warhead miniaturization was the bulky, heavy vacuum tube electronics of the 1950s. Microelectronics resulted in part from programs to miniaturize nuclear weapons. The microelectronics revolution solved most technological challenges of warhead miniaturization long ago for North Korea and for all nuclear missile aspirants.
A nuclear missile warhead also needs shock absorbers to soften forces of acceleration during launching and deceleration when re-entering the atmosphere. A heat shield to penetrate the atmosphere, in order to blast a city, is also necessary — these are technologically simple and within North Korea’s capability.
Indeed, in 2013, a publicity photo by state media of North Korea’s KSM-3 satellite interior shows a shock absorber cage, allegedly for an earth observation camera but suitable for a small nuclear weapon. North Korea recently conducted another illegal missile test demonstrating a re-entry vehicle and heat shield.
The president and the press is missing, or ignoring, the biggest threat from North Korea — their satellites. On February 7, North Korea orbited a second satellite, the KSM-4, to join their KSM-3 satellite launched in December 2012. Both satellites now are in south polar orbits, evading many U.S. missile defense radars and flying over the United States from the south, where our defenses are limited. Both satellites — if nuclear armed — could make an electromagnetic pulse (EMP) attack that could blackout the U.S. electric grid for months or years, thereby killing millions.
Technologically, such an EMP attack is easy — since the weapon detonates at high-altitude, in space, no shock absorbers, heat shield, or vehicle for atmospheric re-entry is necessary. Since the radius of the EMP is enormous, thousands of kilometers, accuracy matters little. Almost any nuclear weapon will do.
Like the frameworks with North Korea and Syria, the Joint Comprehensive Plan of Action of 2015 assumed that Iran would fulfill its obligations and open its facilities to inspectors. The JCPOA assumed that Iran would moderate its behavior and join the international community. Yet unlike its North Korean and Syrian allies, Iran was the largest state sponsor of terror and openly vowed to destroy another state—Israel. Unlike them, Iran systematically lied about its unconventional weapons program for 30 years. And unlike Damascus and Pyongyang, which are permanently barred from acquiring weapons of mass destruction, Tehran can look forward to building them swiftly and legitimately in the late 2020s, once the JCPOA expires.
This, for Israel and our neighboring Sunni states, is the appalling flaw of the JCPOA. The regime most committed to our destruction has been granted a free pass to develop military nuclear capabilities. Iran could follow the Syrian and North Korean examples and cheat. Or, while enjoying hundreds of billions of dollars in sanctions relief, it can adhere to the agreement and deactivate parts of its nuclear facilities rather than dismantle them. It can develop new technologies for producing atomic bombs while testing intercontinental ballistic missiles. It can continue massacring Syrians, Iraqis and Yemenis, and bankrolling Hamas and Hezbollah. The JCPOA enables Iran to do all that merely by complying. A nuclear-armed Iran would be as dangerous as “50 North Koreas,” Israeli Prime Minister Benjamin Netanyahu told the U.N.