...and
Today, Electors are chosen by popular election, but the Constitution does not mandate a popular election. The 14th Amendment does mention the choosing of Electors, but is relevant only when Electors are elected by popular vote. There is similar mention in the 24th Amendment. In other words, Electors could be appointed by a state’s legislature, or the legislature could empower the governor to choose electors. In some cases, state law allows for such appointments if the popular vote cannot be used to determine a winner, such as if election results are contested up to federally-mandated deadlines.
...plus, with a wink and nod, the political party can suggest the Electors vote for someone else
There is no Constitutional provision or Federal law that requires Electors to vote according to the results of the popular vote in their states. Some states, however, require Electors to cast their votes according to the popular vote. These pledges fall into two categories—Electors bound by state law and those bound by pledges to political parties.
The U.S. Supreme Court has held that the Constitution does not require that Electors be completely free to act as they choose and therefore, political parties may extract pledges from electors to vote for the parties’ nominees. Some state laws provide that so-called “faithless Electors” may be subject to fines or may be disqualified for casting an invalid vote and be replaced by a substitute elector. The Supreme Court has not specifically ruled on the question of whether pledges and penalties for failure to vote as pledged may be enforced under the Constitution. No Elector has ever been prosecuted for failing to vote as pledged.
http://www.archives.gov/federal-register/electoral-college/electors.html
http://www.usconstitution.net/consttop_elec.html