However, if you now realize that you can't bring back all those manufacturing jobs you thought you were going to bring back, then having a shrinking labour pool means there are more of those jobs available for the remaining workers.

The other issue that is not well addressed is the issue of automation. Let's take the concept of self-driving vehicles and the potential of 3 million trucks drivers being out of work in 20 years. If that is the case then the workforce will be shrinking anyways.

Trump can't admit publicly that those jobs will not be coming back or that he will not achieve 3% annual growth or that even if he did, that type of growth does not create the same type of employment levels as it did in the past. Thus, the option is to shrink the labour pool in the short term to make it seem like his base is getting more jobs.