Destined for severe decline in the future of America. Generally speaking unions are becoming less and less working class white and more and more minority based. In political America that generally means dramatic decline in influence on all levels.
Also there are geographical phenomena at play. The Midwest, Northern unions are in decline because manufacturing is being permanently moved to the Southern US and given to lower class Hispanics, blacks, whites, others who aren't even legally allowed to unionize in those states because unions are illegal or near illegal as well as the expected pay is significantly lower in the South. That phenomena is unstoppable at this point. Midwest, Northern manufacturing is being permanently phased out. Soon it will be gone forever due to the above reality.
Union decline can basically be attributed to this phenomena:
-Strong white working class demographics = ability to pressure white middle + upper class to safeguard unions
-Weak white working class demographics + strong minority working class demographics = inability to influence white middle + upper class to safeguard unions = companies relocate to anti-union South + existing unions are gutted into irrelevance
American unions fate was completely reliant on strong white working class demographics and political influence. That has seriously waned and isn't likely to come back. Nor are the unions.