South and North Korea agreed to a pair of "denuclearization" measures in the Pyongyang Joint Declaration -- dismantlement activities at Sohae (Tonchang-ri) and Yongbyon. There are some technical aspects to both that might inform our discussion. (1/17)
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First, the offer to "permanently dismantle the Dongchang-ri missile engine test site and launch platform" is the same offer that Kim made in Singapore. (2/17)
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While North Korea has described this step as a "verification" measure, it does not prevent ongoing ICBM production at Sanum-dong and elsewhere -- nor would it prevent North Korea from resuming ICBM tests which are conducted from mobile launchers. (3/17) 
[Twitter ate the next 14 tweets. Let's try this again.]
North Korea would need a test stand to develop a future liquid propellent engine. But North Korea probably completed the testing cycle for the "March 18" engine prior to the two publicized static tests and the beginning of flight testing for the Hwasong-12, -14 and -15. (4/17)
A new wrinkle is Kim's offer to invite "experts from relevant countries" to watch the dismantlement -- although it is similar to stunts like the demolitions of the cooling tower and the tunnels at Punggye-ri. It has little or no verification value. (5/17)
According to South Korean officials, Moon was the one who proposed "the permanent dismantlement of the nuclear facilities in Yeongbyeon." Kim agreed, although with serious conditions. At least he didn't offer to bring his unicorn to the dismantlement. (6/17)
If that happens, though, there are a lot of facilities at Yongbyon, including two reactors a reprocessing line and a uranium enrichment plant. Note that Kim did not offer to allow @iaeaorg inspectors back in to monitor these facilities. (7/17)
The gas-graphite reactor is 30+ years old, so North Korea might be ready to retire it. Still, old or not, closing the gas graphite reactor and reprocessing line would constrain North Korea plutonium production provided there are no covert facilities. (8/17)
There is also a "light-water" reactor at the site, although we wonder whether it is really just a copy of the gas-graphite reactor with a dome. Recall that North Korea built a camouflaged copy of Yongbyon for the Syrians. Too bad the @iaeaorg won't get a peek at that. (9/17)
North Korea also showed Sig Hecker an enrichment plant at Yongbyon in 2010. We think North Korea built this plant ain the open at Yongbyon and then displayed it was because the plan was to trade it later, while retaining other covert sites. (10/17)
The US believes there are at least TWO other enrichment facilities. One of those is the Kangson enrichment plant, which we identified this summer. If you read the reporting carefully, the US believed there is a third site that we have yet to find. (11/17)
Dismantling Yongbyon would be welcome. But it wouldn't stop North Korea from expanding its arsenal. A freeze would have to cover all the sites and be verified. It would be tricky to devise good enough verification measures that are politically palatable to Kim. (12/17)
The Moon Administration doesn't care about disarmament or verification. It sees these as American concerns. When a ROK official was asked about covert sites like Kangson, he just said: "I don't know." (13/17)
As a result, the North Koreans are offering gestures that mimic disarmament. They don't meaningfully constrain North Korea's nuclear program. But they aren't meant to. There primary purpose is to appease Trump, so that Moon and Kim can keep their engagement alive. (14/17)
The thing is, at the moment, mimicry is sufficient. Trump is appeased by Kim's gestures, even if his description of what was agreed is comically inaccurate. (There are no nuclear inspections, for example.) (15/17)
As I've said before, it iok if Trump tacitly accepts North Korea's status as a nuclear power, which was probably inevitable anyway. This is what an Israel-style deal looks like with North Korea: They pretend to disarm and we pretend to believe it. (16/17)
foreignpolicy.com/2018/09/18/you…
foreignpolicy.com/2018/09/18/you…
But the problem, as @sbg1 mentioned in her @NewYorker essay, is that no one on Trump's team is in favor of this. So is it really sustainable? I still worry Bolton will convince Trump that he has been cheated by Kim and looks the fool. And if that happens -- watch out. (17/17)
