Until polls close on Election Day, millions of people across the United States are casting ballots for their preferred candidates to succeed President Biden in the White House. But determining the winner is not as simple as totaling up how many people voted for Vice President Kamala Harris or former President Donald Trump, because of the Electoral College.

The Electoral College is a controversial step in the U.S. election process that dates back to the 18th century. While there's a growing movement to try to get rid of it, others defend the system that gives some states more weight in presidential elections.

Why was the Electoral College created in the first place?

Whether the Electoral College is fair or necessary is subject to fierce debate that in some ways dates back to its founding.

The concept emerged during the Constitutional Convention, which took place over a four-month period in 1787 to address issues with the early system of government in the United States. State delegates who attended the convention were divided in their views on how the country should elect its president, with some suggesting Congress should choose the executive and others advocating for direct democracy, where citizens would vote to elect their leader. At the time, the right to vote was almost entirely restricted to White men who owned property.

What to do about the method for selecting a president became a lingering debate at the convention, said Michael Thorning, director of the Bipartisan Policy Center's democracy project, who told CBS News the issue was finally passed off to a group tasked with resolving prior disagreements over certain areas of the Constitution. It was called the Committee on Unfinished Parts.

Committee members settled on the Electoral College as a compromise.

"There were some attendees of the Constitutional Convention who did not trust the popular will as much," said Thorning. "They were concerned that you would be asking people with very little political experience, knowledge of the candidates, understanding of their platforms, to select someone that they may not know. And so they may just vote only for the person whose name they recognize, versus the most competent candidate. So, this was a bargain."

Population size was a major point of contention. Delegates who attended the convention came from large states, like New York and Pennsylvania, and small states, like New Jersey and New Hampshire. While some of the larger states would have favored an election system driven by the popular vote, which would give them a greater say in the election than a state with fewer voters, Thorning said delegates from some smaller states had concerns about being "overrun" by more populous neighbors.

Other large states that sent delegates to the Constitutional Convention had institutionalized slavery. At the time, hundreds of thousands of people were enslaved across the South, amounting to about 40% of the Southern population. Under the notorious "three-fifths compromise" decided during the same convention — which allowed Southern states to count three-fifths of their enslaved populations in their total census — slave-holding states could have considerable power in the House of Representatives and the Electoral College, even though only a fraction of their residents were allowed to vote.

Why do electoral votes matter for presidential elections?

Elements of the Electoral College have changed since the Constitution was drafted, since voting rights expanded and citizens choose their state's electors. But its fundamental role in picking the president has remained.

"We have 50 state elections all individually happening," said Thorning. "What's important is who wins each of the 50 state elections."

Electors are allocated to each state roughly based on its population, with the number of electors equal to the state's total number of U.S. senators and House members in Congress. That means even the least-populated states get three, while many states have a dozen or more; the state with the largest population, California, currently has 54.

In most states, it's a winner-take-all system where all of the electoral votes go to whichever candidate won a majority of the popular vote in the sate. Only Maine and Nebraska have slightly different systems for dividing up their electors based on who won at the congressional district level.

There are 538 electors who will case votes in the Electoral College, and a presidential candidate needs to secure at least 270 of those votes in order to win.

It's possible to win the popular vote nationwide but still lose the election, if states with enough electoral votes go the other way.

This system also means candidates end up focusing a disproportionate amount of their time and funds on campaigning in a small number of battleground states that could tip the balance in their favor.

Why do we vote if there is an Electoral College?

When voters cast their presidential ballot, they're actually choosing the group of electors who on good faith will represent the political party is affiliated with their preferred candidate. The people who fill these roles are selected by their party and are typically local officials or committed political supporters.

Thorning called the popular vote for president "a really unofficial gauge of the election."

"While voters go to the polls and see a presidential candidate on the ballot, they are actually voting for electors who represent those people," he said. "Whoever the prevailing electors are in those elections, they are the people who ultimately cast the Electoral College votes. So, the post-election period, really, is a process of translating these many popular vote elections into the Electoral College."

After the November election, the electors gather in each state in December to formally cast their votes for their state's winner.

Why do some critics want to get rid of the Electoral College?

Critics of the Electoral College primarily take issue with the fact it leaves open the possibility that the outcome may not reflect the results of the popular vote. This happened most recently in 2016, when Trump won the presidency with a majority of Electoral College votes despite Hillary Clinton, the Democratic nominee, winning the nationwide popular vote by almost 3 million.

Similar conundrums played out in a handful of presidential elections before, including in 2000, when George W. Bush won the Electoral College despite losing the popular vote to then-Vice President Al Gore. In that race, the popular vote split between Bush and Gore by a very small margin — much narrower than in 2016.

"Over time, the world has evolved, even while the Electoral College has not evolved so much," said Thorning. "I think by some standards, the idea that it is not a direct popular vote for president in modern times does strike some people as not being democratic."

Under one proposed alternative, called the National Popular Vote Compact, states would agree to give their electoral votes to whichever candidate wins the national popular vote — even if it doesn't match the outcome in their state.

Minnesota Gov. Tim Walz, Harris' vice presidential running mate, recently spoke out against the Electoral College, saying "we need a popular vote" during a campaign event in California.

"I think all of us know the Electoral College needs to go," Walz said. "But that's not the world we live in. So we need to win Beaver County, Pennsylvania. We need to be able to go into York, Pennsylvania, and win. We need to be in western Wisconsin and win. We need to be in Reno, Nevada, and win."

The Harris-Walz campaign followed up with a statement saying his comments did not reflect their official position on the issue.

Thorning pointed out that while the Electoral College system is partly enshrined in the Constitution, it can be amended.

"I think we should continue to debate aspects of our democracy and what's in our Constitution," Thorning said. "But at the end of the day, this is the system so far that we've agreed to, and so we have to conduct our politics through the system that we have, and conduct change to that system through the system that we have. There is a way to make that change, if there is support for it."