Some form of early voting is in place in most states across the US, meaning much of the electorate will have cast their ballot before election day.
Although those votes are not counted until polls close on Tuesday, some states release data on the number of early votes and how many were from registered Republicans or Democrats.
In Nevada, for example, we know that of nearly 800,000 votes cast before early voting closed on 4 November, 42% were by registered Democrats while 36% were by registered Republicans. Those numbers aren't too different to 2012, when Barack Obama took the state with a winning margin of 6.7%.
Of course, there's nothing to say that those registered with one of the parties will definitely vote that way, especially since both Mr Trump and Mrs Clinton have made direct appeals to supporters of the other party who may be disillusioned with their candidate.
But in general, the Nevada data comes as a surprise, because much of the recent polling in the state has suggested Donald Trump is in the lead. That doesn't necessarily mean the polls are wrong - Mr Trump could have a groundswell of support on election day - but if they are, it may suggest they are finding it hard to account for the surge in Hispanic voters.
That Hispanic surge has been noticeable in several states, including Arizona, Colorado, Florida and North Carolina, according to analysis by Catalist, a data firm working for Mrs Clinton campaign team.
In previous elections it has been less clear who Hispanic voters would back (Republican President George W Bush won 40% of their votes in 2004), but this year it is clearer thanks in part to Mr Trump's tough rhetoric on immigration and Mexicans. Research group Latino Decisions projects that 79% of Hispanic voters will support Hillary Clinton.
One thing we know for sure is that far more people have voted early in this election than in the past. In 2012, the total number of early votes cast was just over 32 million. So far, more than 40 million people have voted early in 2016.