It's not 'us' versus 'them.' The Rust Belt white working class used to be a robust part of the Democratic Party. They are 'us'. Economic hardship is well-known to encourage racism and xenophobia. These people are hurting, they were our allies, and they need help. These hateful cries are cries of pain.
Whether Trump's tax plan will actually benefit them or not, is the question. Increasing the distance between the affluent and the working class through 'beneficial' tax cuts is not necessarily a good start.
But much is yet to be decided. Wait and see.