Both campaigns have deliberately bypassed rational argument. They play instead to the emotional response of angry people for whom reason no longer makes sense. Since the time of Plato and Aristotle, democracy's critics have warned of the ease with which reason can be subverted and citizens seduced by the false oratory of charismatic leaders.
The answer is they probably won't be able to and that in itself is a catastrophe. In such vitriolic times the country needs Parliament to function properly, especially with a government just entering its infancy, something it will not be able to do without a unified opposition. Labour needs to sort itself out and quickly, for the sake of us all.