The most extraordinary and unconven¬tional presidential election in modern times is approaching the finish line on Nov. 8. Voters, and indeed the general populace, are fed up with “politics as usual” and have voiced anguish about the choices for president. Their expectations for political transparency, accountability and trustworthi¬ness have changed. This election may well be the first where more voters cast ballots against a candidate rather than in support of one, and polls confirm that Americans are paying close attention.

Both Republican candidate Donald Trump and Democratic candidate Hillary Clinton have used a campaign strategy of tearing each other down as opposed to emphasiz¬ing why they would be the better president. But scandals, verbal missteps and disparag¬ing ads have only served to reinforce voter disillusionment. Whoever wins this election will have a tough time governing, especially with a party split in Congress.

A stacked Electoral College

In the U.S., voters don’t directly elect the president (or vice president). Instead, the country uses a system where “elec¬tors,” based on the number of each state’s congressional representation (Senators and Representatives), are designated to vote for the president. So, to win the presidency, the candidate must get a majority of 270 Elec¬toral College votes (435 Representatives, plus 100 Senators, plus three for the District of Columbia). Campaign strategies conse¬quently are not necessarily designed to win the national popular vote, but instead to gar¬ner a majority of the Electoral College vote in critical battleground and swing states.

The graphic shows each state’s presi¬dential electoral outcomes for the past four general elections. Twenty-one states have voted for the Republican candidate, result¬ing in 180 Electoral College votes. Eigh¬teen of the states voted for the Democrat, but they resulted in 242 Electoral College votes—only 28 shy of what’s needed to win the election. During this period of four elec¬tions, 10 states have switched voting results with a total 118 Electoral College votes.

The challenge for the GOP is obvious: Its candidate cannot afford to lose more than a couple of these swing states. And, losing Florida with 29 Electoral College votes (presuming the Democratic voting trend holds) means the Republicans must win in the other swing states and somehow land a few traditional “blue” Democratic voting states. Voting trends are shifting in several traditionally “red” Republican states, most notably in Virginia, Colorado and North Carolina, which are becoming more blue, Democratic-leaning states. For this 2016 election, a few other “in-play” states have emerged, namely Missouri, Nevada and (possibly) Pennsylvania.

Looking at the latest voter surveys, Trump’s pathway to the White House is extremely narrow. His campaign has shifted resources and media ad buys to reflect the critical nature of key states like Florida, Pennsylvania, Arizona and North Carolina. The Electoral College map and Clinton’s more formidable funding are significant challenges.

Voter turnout is key

While impossible to forecast, this elec¬tion hinges on whether voters come out in typical numbers to cast ballots against one of the candidates, or decide to stay home in dismay over the campaign rhetoric and mud-slinging. Fundamentally, the election is about support of an establishment candi¬date—Hillary Clinton—versus upheaval of the political status quo via the candidacy of Donald Trump. Both candidates’ continuing unfavorable ratings make this a very diffi¬cult choice for voters (or exceptionally easy, depending on their visceral feeling).

If voter turnout stalls, the election could be rather close along historical margins (2% to 4% spread). If voters flock to the precinct booths, then it likely turns into a rout for Clinton based on demographics and urban shifts. We will likely know which way the voting turns fairly early on election night as the key Electoral College swing states in the Eastern time zone report results.