Biden was already the presumptive presidential nominee, after Bernie Sanders suspended his campaign. Wisconsin controversially held in-person voting despite the pandemic.
Though the Vermont senator did not emerge as the Democratic nominee in either of his two bids, his campaigns have reshaped the party's politics and policy in significant ways.
One of the hardest decisions for any candidate is whether to drop out of a race. It's even harder for the Vermont senator, who, at 78, likely wouldn't run for president again.
Gov. Tony Evers tried to postpone voting and extend the absentee deadline, but he was blocked by courts. Results for Tuesday's contests are not expected for days.