The dockwoker's union used to be a lot of people and thus had a lot of influence. Due to automation, it's now a small group of people earning way above-market salaries. As automation increased, the union negotiated for better salaries in exchange for decreasing the number of workers. They're able to keep their high salaries and benefits by holding the rest of the economy hostage during a strike.

Trump should pull a page from the Reagan playbook. Break the union, hire replacements, like Reagan did with the air traffic controllers. Trump isn't President right now, so he can't do this.