The Republican Party has never liked labor unions, and they have fought against them for decades. While the Democrats controlled Congress, the GOP war on unions wasn't successful. But about 1980, with the election of Ronald Reagan, the Republicans gained enough power to start chipping away at union power in the country. That, and a very effective propaganda campaign by them against unions (which had started years earlier), allowed them to reduce both the power of unions and the membership in those unions. That was disastrous for the American middle class.
The chart above (from the Economic Policy Institute) shows the effect unions had on the sharing of rising productivity (in the form of rising wages), and the effect of the decline of unions. Note that as union power grew, rising productivity was shared between companies (i.e., the top 10% who owned those companies) and workers. Both groups benefitted, and it helped to create a vibrant and growing middle class in this country.
But as the Republicans chipped away at the power of unions and the right of workers to unionize, the share of rising production that went to the top 10% grew and the share that workers got decreased. It has gotten to the point that the share of income going to the top 10% has reached levels not seen since the 1920's. And the share going to workers has stagnated.
This has resulted in the largest gap in income between the rich and the rest of America since the 1920's, and it's still growing. The recent Republican tax plan (which gives huge cuts to the rich and not much to workers) will stimulate the growth of that income gap even faster.
The Republican attacks on unions (and their massively unfair tax plan) are nothing less than a class war -- undertaken on behalf of the rich and against the working and middle classes. And it is resulting in a huge redistribution of income -- from most Americans to the richest Americans.
We must change this before we see a replay of the Great Depression. And the only way to do that is to kick the GOP out of power. We must flip Congress to control by the Democrats in November of 2018 -- and then hold Democratic feet to the fire to change economic and tax policy to be fairer to all Americans.