It doesn't happen often, but Twitter delivers some pretty useful insights on occasion. Though I remain unconditionally opposed to the ridiculous "threading" format – seriously, just get a blog already – this string of posts by Matthew Chapman offers a useful way of conceptualizing Trump's worldview in terms of negotiating.
Briefly, he is a con man. Like many con men, he presumes that everyone else is also a con man. This is how many Wall Street and real estate types morally justify their behavior – I am doing nothing wrong by ripping you off, since the entire economy is everybody trying to rip everybody else off.
Since everyone is trying to rip everyone off, a deal in which the other party is enthusiastic is de facto evidence that you have been ripped off. Nothing can be mutually beneficial, even though making mutually beneficial transactions is like, the Page 1 definition in every textbook ever written about a market economy or even a barter system. Nope. The other party being pleased with the arrangement means you got fucked, period.
Therefore every "deal" the United States has ever made with another country is bad, because if the United States was not getting fucked then the other country would not have wanted to make the deal.
God only knows what really goes on in that desiccated brain of his, but this is one potential explanation that lends a bit of coherence to his insistence on pulling the United States out of NATO, out of the Iran deal, out of treaties, out of free trade agreements, out of everything. Either the other country is clearly getting fucked, or we are. No other outcome can exist.