The Wisconsin primary was held on Tuesday.
Joe Biden has a 20-point lead over Sanders.
According to NPR, Sanders supporters are fervent and fed up.
Sanders' path to the Democratic nomination is getting narrower every day.
Biden has a 1,217-to-914 delegate lead over Sanders.
To be the nominee, a candidate needs 1,991.
That means Biden needs just 46% of the remaining delegates to be the nominee.
Sanders needs at least 64% to secure the nomination.