Automation was reducing the number of manufacturing jobs. But "free trade" has taken away a lot of the manufacturing itself. The US as a whole can no longer make the TVs and iPhones that it consumes so many of.
It doesn't make low value-added goods like TVs, it doesn't employ a lot of people, and it's not growing as fast as other sectors, but we still manufacture more than ever before.
The “crumbling” sensation is because fewer people are employed by it and more people are employed (and earning more) in other sectors.
Yes, aerospace and military tech are the biggest manufacturing industries in USA... Quite profitable these days with all these conflicts...