"lowering the corporate tax rate will open up employment opportunities for the poor."

That might be true if we were in a capital-constrained economy. We aren't. Corporations and banks are sitting on billions and billions of cash, giving them more money isn't going to make them expand business. What they will do with more money is invest it where the can get the best return, and that is in higher growth markets overseas. 

We are in a demand-constrained economy. Businesses will expand in a response to increased demand.