It is interesting that the left has made heros of the working class; now those people have rejected the left they are called deplorables. Perhaps that is why Marx called for a dictatorship of the proletariat.
The left automatically opposes President Trump even on issues they previously supported. As you say, they used to be for the American working class. Now that President Trump is working on bringing those manufacturing jobs back, they are free traitors.
The modern left plays lip service to the working class. They have been hijacked by privilaged middle class metropolitans who actually despise the working class, and view them as racist, stupid gammons and deplorables. They fetishise immigrants and ethnic minorities and can barely conceal their contempt for the indigenous working class Britons (or Americans in the US).
Unfortunately for them, the white working class still vastly outnumber their prefered demographic groups, and immigrants without citizenship cannot vote, so they pissed all over the wrong people in their quest to attain power.