What Unions *should* do is become a partner with the businesses and work together to lower costs of manufacturing. By doing so, there will be a stronger job market and more money to hire new employees or give raises to existing ones.
As is, the Unions make is difficult and more expensive for the businesses to run. It also makes it possible for a poor performer with seniority to keep their job over a strong worker who is lower on the list.
The Unions could work the angle of co-employment and take the HR and benefits burden off the employers (similar to what ADP TotalSource does). They could keep the Unions financially healthy by charging a fee, and reduce the employment expenses by having a central area for employment resources for all the companies that they co-employ with. These actions would truly benefit the worker, strengthen the business and secure more US jobs.
But, they don't. Instead they view the companies as evil and do what they can to divide employees and employers. So, we continue on our downward slope and keep losing jobs.