WHY was it booming ?
Give you a hint. Name a large, highly populated 1st world country, with large amounts of natural resources and mature industrial sector and infrastructure that was NOT bombed during WWII. So the USA was able to build stuff for the rebuilding of Europe and Asia. It could invest in R&D rather than in schools, hospitals, houses, roads, rail, water, electricity.
Its not about America being great again, its about the rest of the world no longer being dependant on America.
In the 1950s the USA was about 60% of the entire worlds GDP, now its about 20% and falling.
The USA only makes up about 4% of the worlds population, so there is still a lot of room to fall yet.
Build your walls, have a trade war, stop immigration, its just going to hasten the fall.
The rest of the world agrees with Trump "No deal is better than a bad deal", and few countries (if any) now have to accept a bad deal from the USA.
Sure loss of trade with the USA will hurt, for a wee while, but other countries will step in and life will continue as before.
No one HAS to buy from the USA anymore, there are alternatives.