Here's what faithless electors are and what they could mean for the outcome of the presidential election

When you go to the polls to "elect" a president, you are actually voting for a particular slate of electors who cast ballots for president and vice president.

The Electoral College is widely known as a "winner take all" system because the winner of the popular vote in each state gets all of the state’s electoral votes. That is, with the exception of Maine and Nebraska, which award their electoral votes more proportionally.

But what happens if electors who are pledged to vote according to the statewide or district popular vote pick someone else? That's called a "faithless elector."

Here's what they could mean for the outcome of the 2020 presidential election.

How are electors chosen?

The Electoral College is made up of 538 delegates. The total number of electors represents the total number of U.S. senators, 100 (two per state); the total number of state representatives, 435; and three more electors for the District of Columbia.

Prep for the polls: See who is running for president and compare where they stand on key issues in our Voter Guide

Each state has a number of electoral votes equal to the combined total of its congressional delegation, and each state legislature determines how it will select its own electors, according to the National Conference of State Legislatures, a nonpartisan association of legislatures.

According to the association, the two most common methods that states use are nomination by state party convention and by state party committee. The parties typically select members "known for their loyalty and service to the party," such as party leaders, state and local elected officials, and party activists.

In some states, the electors' names appear on the ballot along with the names of the candidates for president and vice president, according to the association.

Explainer:Why can the Electoral College pick a president who got fewer votes? 

When does the Electoral College vote?

The electors meet in their respective states to cast a ballot for president and a second for vice president.

Electors cast their ballots on the Monday after the second Wednesday in December of the presidential election – about a month after Americans cast their ballots in the popular vote. This year, electors will meet on Dec. 14.

It takes 270 or more electoral votes to win a presidential election.

Can Electoral College really tie? Yes. It's not likely but here's how it works

Which states have laws against faithless electors? What does the Supreme Court say?

The Constitution and federal law are silent on the matter, but some states have passed laws that require their electors to vote as pledged. In July, the Supreme Court ruled in favor of these laws.

"The Constitution’s text and the nation’s history both support allowing a state to enforce an elector’s pledge to support his party’s nominee – and the state voters’ choice – for president," Associate Justice Elena Kagan wrote in an opinion.

During the last oral argument of the court's term in May, justices on both sides of the ideological aisle expressed concern that electors could be bribed, particularly by the losing party in a close election.

"The Supreme Court made it clear that the elector is not there to vote his or her conscience. The elector is there to vote how the state dictates," said Erwin Chemerinsky, dean of the University of California-Berkeley Law School. "Most states now forbid faithless electors."

Supreme Court rules:Presidential electors can be forced to uphold popular vote

At least 32 states and the District of Columbia have laws that attempt to bind the votes of electors. Those states are Alabama, Alaska, Arizona, California, Colorado, Connecticut, Delaware, Florida, Hawaii, Indiana, Iowa, Maine, Maryland, Massachusetts, Michigan, Minnesota, Montana, Nebraska, Nevada, New Mexico, North Carolina, Ohio, Oklahoma, Oregon, South Carolina, Tennessee, Utah, Vermont, Virginia, Washington, Wisconsin and Wyoming.

In some of those states, rogue electors can be replaced or fined.

"Most of them do not have an enforcement mechanism, and the ones that do often simply punish the elector instead of purporting to correct the vote," said Kermit Roosevelt, a law professor at the University of Pennsylvania Law School.

How common are faithless electors?

Faithless electors are not common, and they've never changed the outcome of a presidential election, according to FairVote, a nonprofit that advocates electoral reform.

Only one elector has cast a vote for the opposite party’s nominee instead of their own in a close contest, in 1796, according to the organization.

Of the more than 23,000 electoral votes counted across 58 presidential elections, only 90 electors have cast "deviant" votes – not ordinary votes for the presidential nominee of the elector’s political party, according to FairVote.

"Faithless electors in the past ... have generally been trying to make a statement, not to change the result," Roosevelt said. "In 1968, a North Carolina elector voted for George Wallace instead of Richard Nixon, but said explicitly later that he wouldn’t have done this if it would have changed the outcome."

What happened in 2016?

There were an unusually high number of faithless electors in 2016.

That year, Donald Trump won with 304 electoral votes. It was the fifth time in American history that the winner of the presidential election lost the popular vote. And it was the second time since 2000 – when Al Gore won the popular vote but George W. Bush won the Electoral College – that a candidate lost the popular vote but won the Electoral College.

Ten electors were disloyal or tried to be in 2016. Eight were Democratic electors – from Colorado, Hawaii, Maine, Minnesota and Washington – and two were Republican electors, both from Texas.

More than 4.5 million people signed a petition advocating for electors to have a change of heart.

"There were an unusual number in 2016 because there was a movement to try to get the electors to exercise independent judgment — either in order to throw the election to Hillary Clinton because she won the popular vote, or in order to make the House of Representatives resolve the election," Roosevelt said.

Could faithless electors change the 2020 presidential election outcome?

Roosevelt said he doesn't expect to see any faithless electors this year, especially after what happened last cycle.

"Electors are usually chosen pretty carefully, and after the 2016 election put a spotlight on them, I think the parties were probably even more focused on ensuring that they chose reliable people," he said.

Chemerinsky said the Supreme Court's decision "might decrease" the likelihood of there being any faithless electors this year.

Still, faithless electors could alter the outcome of a close election, Roosevelt said.

"If we do end up with a close electoral vote, we could easily see a similar campaign to influence the votes of electors, but I don’t think it would succeed," Roosevelt said.

Richard Pildes, a professor of constitutional law at the NYU School of Law, said the topic of faithless electors was "not the issue for now."

Chemerinskyadded that it's "potentially an issue, but, at this point, there are so many more salient questions to be resolved.

"Who’s going to win Georgia, Arizona, Pennsylvania?"

Contributing: Richard Wolf