Who cares whether Mexicans will pay for the wall or not? The cost is peanuts, relatively speaking. Who cares even whether the wall is built or not? As shown by most of the other countries, the wall is not necessary to protect the borders.
What Trump has done, is what is called in negotiations "moving beyond the sale." We are discussing who pays for the wall, practically accepting that the borders should be secured one way or another. Before Trump, it wasn't accepted by the establishment in all three parties, including libertarians.