Here is a graph from NPR that shows, over time, the number of jobs classified as either manufacturing and service.
A few observations:
(1) One problem I have with it is the numbering on the vertical axis. The red line representing manufacturing jobs hugs the 20 million mark but it does appear over it more than under it. Because the measurement scale is small it is hard to see that even small changes represent 100's of thousands and/or multiple millions of jobs gained or lost in a given time period.
(2) The sum total of manufacturing jobs has stayed within a pretty constant/consistent band over time, with the exception of the Great Depression and Great recession. It has had its ebbs and flows.
(3) Look at the two historical points I put on the graph (1960 and 2009-ish). Both are at 20 million manufacturing jobs. However, in 1960 the civilian labor force was 69.63 million so those 20 million manufacturing jobs represented 29% of the labor force. In 2009 the civilian labor force was 157.7 million so those 20 million represented 13% of the labor force (data source HERE).
Politicians and Policy Makers focus a lot of attention on the manufacturing sector in terms of how to promote jobs. Given the history of the nominal number of jobs in this sector, is this a proper focus or a misplaced one?