Article II Section I of the United States Constitution provides the manner in which the executive power of the United States is to be granted to a President and Vice President. "Each State shall appoint, in such Manner as the Legislature thereof may direct, a Number of Electors, equal to the whole Number of Senators and Representatives to which the State may be entitled in the Congress."
Each state is granted two Senators. The House of Representatives is allocated by a process known as "reapportionment" based on population changes as recorded each decade by the Census.
A slate of Electors representing the number of Representatives and Senators of each state then vote based on the popular vote of that state. For example the state of Maryland has two Senators and eight Representatives which gives the state of Maryland a total of ten electoral votes. When the general population of the state of Maryland vote for the President of the United States the majority vote for that candidate is the person the Electors cast their vote for.
The Electoral College protects against voter fraud on a national level. It is almost impossible on a national level to completely stop or abolish voter fraud. The Electoral College process keeps voter fraud in check. For example the largest cities within the nation tend to sway for a particular political party. Voter Fraud would increase and be practiced and encouraged within certain areas of the nation if the Electors of the Electoral College were forced to cast their vote for the candidate that won the national level popular vote. The Electoral College reduces the impact of voter fraud within the Nation.
James Wilson (1742-1798), delegate from Pennsylvania and member of the Constitutional Convention concerning the Electoral process stated, "By it we avoid corruption; and we are little exposed to the lesser evils of party intrigue... The Constitution, with the same view, has directed, that the day on which the electors shall give their votes shall be the same throughout the United States... With this regulation, it will not be easy to corrupt the electors, and there will be little time or opportunities for tumult or intrigue."