What’s at stake
Donald Trump essentially won the presidency in 2016 thanks to a relatively tiny number of votes in three states: Pennsylvania, Michigan and Wisconsin, between them coming to 46 electoral votes. If he loses any of them, he will be in trouble, and Wisconsin – the least anticipated victory of the three last time – would be a major symbolic blow as well as an electoral one.
Last time around
Hillary Clinton lost Wisconsin to Mr Trump by a mere 22,748, or 0.77 points. While not her narrowest loss – that came next door in Michigan – it was one of the results that led the networks to call the election for Mr Trump. Ms Clinton infamously did not campaign in the state in person; she and others from her campaign have cited a wealth of internal data that indicated she should be better deployed elsewhere.
Read more: Should you trust the polls in 2020?
On the ground
Mr Trump has lately been boasting at rallies that thanks to his administration, the US is “rounding the turn” on the coronavirus pandemic. But in Wisconsin, that is not true – at least not in a good way. Cases, hospitalisations and deaths are all on the rise in the state, which has become one of the most acutely affected of the current wave of new infections.
Whether this will dent Mr Trump’s chances is unclear, but the way things stand, the deck is starting to look stacked against him anyway.
The home stretch
Unsurprisingly given its role in 2016, both Mr Biden and Mr Trump have paid sustained attention to the state. Mr Trump gave a rally in Green Bay on Friday, but Mr Biden is ahead of him Trump in most polls – in some of them by a long way.
Read more: The Electoral College, explained
But the Democrats have learnt from 2016 that they have no room for complacency. Among their biggest worries is voter suppression: the state has a recent history of removing people from voter rolls and imposing tough new rules to make voting and registering harder, and in particular harder for Democratic-friendly areas and demographics.
The US Supreme Court has refused to extend the deadline for absentee ballots to arrive, meaning that any ballots posted too late to arrive by election day will not be counted. The Democrats are now embarked on a campaign to make sure anyone who has requested a postal vote but not returned it yet turns it in by hand before 8pm on 3 November.