On Nov. 3, the popular vote will directly decide the winners of races up and down the ballot, except for one.
While voters elect members of Congress, occupants of governor's mansions, state legislators, mayors and other local officers, the nation's highest office is determined by the Electoral College -- an obscure and controversial feature of America's electoral system established by the Constitution.
In every presidential election, dating back to the country's first in 1789, voters cast their ballots for a slate of electors, who are often party loyalists nominated by a state's political party to pledge support to the nominee.
The two presidential candidates jockey for the needed 270 electoral votes of the 538 total at stake to clinch the White House. With some states solidly in Republicans' or Democrats' corner, the focus on the electoral map typically narrows to the key battlegrounds -- a collection of states that are likely to tilt the election in one candidate's favor.
Here's what to know about the Electoral College:
Why the Electoral College?
In 1787, the primary conflict between delegates at the Constitutional Convention in Philadelphia was over the process for electing the president. With dueling plans over either empowering Congress or a popular majority with the ability to elect the chief executive, the Founding Fathers ultimately settled on the Electoral College as a compromise.
Since inception, the Electoral College has been a quirk in the country's voting process -- a group of electors who reflect the distribution of power across the states, based on congressional representation.
In this engraving, Benjamin Franklin is depicted speaking at the 1787 National Convention held in Philadelphia.
The system was designed to both balance sectional interests between the north and south -- a divide that "mapped" the slavery issue -- and to shield the separation of powers by not giving Congress outsize influence over the presidency, said Richard Pildes, a professor of constitutional law at New York University and an expert on election law.
"Southerners wouldn't stand for direct popular election of the president because slave states would get no credit for their human chattel," wrote Akhil Amar, a professor of law and political science at Yale University, in his book, "The Constitution Today: Timeless Lessons for the Issues of Our Era."
The indirect pathway to the presidency also insulated the choice for the president from the throes of "factions," which James Madison warned against in the "Federalist Papers" as a group he viewed as "united and actuated by some common impulse of passion, or of interest, adversed to the rights of other citizens, or to the permanent and aggregate interests of the community." And in the absence of "national familiarity" with potential picks, the mechanism thwarted concerns among the founders over 18th Century voters not knowing much about the candidates, Pildes said.
The system, the framers decided, was a middle ground between electing the president by Congress and by a popular vote, and would be a quadrennial institution of electors that only met in their individual states, making "it harder to corrupt the process," Pildes said, as some feared foreign interference.
Who are the electors?
Every four years, both political parties choose their electors in the months before the election to cast votes at a meeting set for the "Monday after the second Wednesday in December of presidential election years," which falls on Dec. 14 this year, according to federal law.
The electors meet in each of their respective states and the nation's capital to cast separate ballots for president and vice president at places determined by the state legislature. The candidates who receive a majority of the vote are formally elected to the White House.
The process for choosing the electors varies by state, with some nominating their electors at party conventions, while others leave it to voters to elect them during the primary process.
"We have no uniform national system for appointing Electors, which means the legislatures do not have to consult the public at all," wrote James W. Ceaser, a professor of politics at the University of Virginia, and Rep. Jamie Raskin, D-Md., for the National Constitution Center.
The electors, who are often prominent figures in each party, are of symbolic import. In 2016, former President Bill Clinton was an elector from New York. This year, Stacey Abrams, the former minority leader in the Georgia State House, will be an elector for the Democratic Party in that state, and Corey Lewandowski, President Donald Trump's 2016 campaign manager, is an elector for the Republican Party in New Hampshire.
How does the Electoral College work?
The president is elected by a college of 538 electors and it takes 270 votes to win.
The number of electors apportioned to states is based on population -- mirroring each state's congressional representation with one electoral vote for each U.S. senator and representative. There is a minimum of three electors per state and the District of Columbia.
In 48 states, plus the nation's capital, electoral votes are awarded using a winner-take-all system, but Maine and Nebraska are different, allowing electoral votes to be split. These two states award one electoral vote to the winner in each congressional district -- with Maine having two and Nebraska having three -- and the remaining two electoral votes are allotted to the statewide winner.
The electors are mostly "conduits for the popular vote in their state," with the December meeting largely being a formality, Pildes said.
Some can break their pledge to vote for their party's nominee, as seven did in 2016, but this has "happened very, very few times in our history," he continued.
The Supreme Court ruled on the "faithless electors" case in July, making it constitutionally permissible to bind electors to vote for the popular vote winner.
Thirty-three states, and D.C., require electors to keep their pledge. In at least five states, penalties exist for defiant votes, while over a dozen states cancel and replace the rogue elector. More laws are likely to be enacted over the coming years to require electors to follow the popular vote, Pildes added.
What happens if there is a tie?
The system has not been without its kinks, particularly in its earliest years.
Before 1804, the second-place finisher became the vice president. A key change emerged after the election of 1800, when John Adams ran against Thomas Jefferson. The vote tally produced a tie between Jefferson and his vice presidential running mate, Aaron Burr, leaving the election up to the House of Representatives to break the tie.
A fierce political campaign ensued with members of the House weighing the lesser of two evils: many Federalists viewed Jefferson as a "principal foe," according to the National Archives, while Burr was seen as nothing more than ambitious. Led by Alexander Hamilton, the House awarded Jefferson the highest office in the land on the 36th ballot and Burr became his No. 2.
Democrats and Republicans lawmakers listen during President Trump's State of the Union address to a joint session of Congress in the chamber of the U.S. House of Representatives in Washington, Feb. 5, 2019.
In the aftermath of the messy contest, the 12th Amendment was ratified in 1804 and separated the votes for president and vice president to avoid a similar outcome.
"It was destabilizing to automatically place the president's biggest and perhaps fiercest political rival in the position of number two, a heartbeat away from the top," Amar wrote in his book. "The effect of the change, however, to redefine the relationship between American's top two officers -- quelling the animosity once built into the system."
Throughout the country's history, there have been only three "contingent elections" similar to the 1800 race.
If no candidate receives a majority of electoral votes, or in the case of a tie, in which each candidate gets 269 electoral votes, the election moves to the House to select the next president under the 12th Amendment. The House only votes from among the top three vote getters.
Each state has a single vote in the House -- giving the party with greater representation in more delegations the upper hand. Under federal law, the process, which has only taken place twice in U.S. history, would play out in early January 2021, ahead of the inauguration.
Republicans currently control 26 delegations, while Democrats hold 22, with one state, Pennsylvania, being evenly split between both parties. But it's the new Congress, which will be elected in November, that determines the all-important vote.
Democrats control the delegations of several competitive presidential battleground states -- such as Arizona, Iowa, Minnesota and Nevada -- by a single seat, while Republicans have a single-seat advantage in Florida.
A presidential candidate needs a majority -- 26 votes -- to win.
The decision for any contested vice president is settled in the Senate, which was the case in the third contingent election in 1837, with each senator casting a single vote. In the upper chamber, a candidate must earn 51 votes to succeed.
If the House remains deadlocked by the inauguration, the vice president-elect will serve as acting president until the House picks a new commander-in-chief.
Can a president lose the popular vote but still win the election?
Four years ago, Trump emerged as the winner of the Electoral College, 304-227, despite losing the popular vote by nearly 3 million votes to Hillary Clinton -- an outcome that has only occurred in five presidential elections: 1824, 1876, 1888, 2000 and 2016.
In 2016, Trump's thinnest margin of victory was in Michigan -- just under 11,000 votes -- yet he won all 16 of the state's electoral votes, and ultimately, the White House.
In the contested election of 2000, which involved an infamous Supreme Court decision over Florida's votes, George W. Bush prevailed by winning the Electoral College, 271-266, over Al Gore, who won the popular vote by more than 500,000 votes.
Screens in Times Square show election results declaring Donald Trump to be President-elect on Nov. 9 2016, in New York.
With a winner-take-all apparatus in most states, the results of the Electoral College and the will of the plurality of voters across the country have at times diverged -- fueling calls for the entire system to be replaced.
Will the Electoral College last?
Over the last 200 years, more than 700 proposals have been introduced in Congress to reform or eliminate the Electoral College, according to the National Archives, without any succeeding.
The closest Congress came to dismantling the Electoral College occurred in the late 1960s-early 1970s, when the House decisively passed an amendment to abolish the system -- the only time a chamber of Congress approved such an amendment. But it died in the Senate after being filibustered by a group of lawmakers from southern states.
Last year, throughout the competitive Democratic primary that ultimately crowned former Vice President Joe Biden the winner, some of the more progressive contenders made scrapping the Electoral College a plank of their campaign platform.
"My view is that every vote matters. And the way we can make that happen is that we can have national voting and that means get rid of the Electoral College," Sen. Elizabeth Warren, D-Mass., said in March 2019.
Similar to Warren, some view the Electoral College as "an artifact of a different time that should change," Kimberly Wehle, a professor at the University of Baltimore, said last month.
More than three-fifths of the country, 61%, support replacing the Electoral College with a popular vote system, a Gallup poll found in September, but there are fissures starkly along partisan lines. Democrats are nearly four times as likely as Republicans to back shifting to an election decided by a popular vote.
Indiana representatives to the Electoral College sign paperwork to officially cast votes for President-elect Donald Trump at the Statehouse in Indianapolis, Dec. 19, 2016.
For a few decades before the 2016 election, most viewed the Electoral College as tending to favor Democrats, Pildes said, but in the aftermath of the last presidential contest, the system is now seen as advantaging Republicans.
"That was partly because the Democrats supposedly had this 'blue wall' of these states that they were just going to win in every election that ran through the Midwest," Pildes said. "As we saw in 2016, once that blue wall could be broken, the view has moved."
Eliminating the Electoral College entirely would be an arduous endeavor since it is hard-wired into the Constitution and would require a constitutional amendment, which involves approval from either two-thirds of both chambers of Congress or a constitutional convention called by two-thirds of state legislatures, followed by ratification by three-fourths of the states.
The other route would be altering the existing framework, without changing the Constitution.
At least two pathways for reform include states modifying their individual laws for allocating electors -- for example, moving to a proportional basis -- or states signing onto the national popular vote interstate compact.
The latter is a state-based effort that seeks to get enough jurisdictions to enact a bill that pledges electoral votes to whomever wins the popular vote nationally. At least 16 states, home to 196 electoral votes, have joined the compact. The bill won't take effect until the states reach 270 electoral votes.
"The Electoral College is now kind of out of keeping with contemporary views about what democracy should mean. I think we're the only major democracy that elects its chief executive in this indirect way," Pildes said.
ABC News' Benjamin Siegel contributed reporting.
