What Is the "Unit Rule" and What Is Its Significance

What is the "unit rule" and what is its significance to the presidential election process? Identify states that do not take part in the unit rule and describe how the process differs. Do you think the presidential election results would differ if states moved away from the unit rule and adopted a process by which the popular vote winner in each congressional district received the electoral votes from that district, and the two votes that derive from the state's senate seats are awarded to the statewide popular vote winner? Explain why or why not.