Think of it as Super Postponed Day.
June 2 had been an afterthought on the Democratic primary calendar. Ever since Joseph R. Biden Jr. seized the mantle of front-runner, voters in New Jersey and a few other states scheduled to vote that day assumed the Democratic horse race would be over before their primaries rolled around.
But with numerous states pushing back voting to June 2 because of the coronavirus pandemic, the date has gained sudden prominence. It now confers a huge bounty of delegates, second only to Super Tuesday in early March, with Indiana, Pennsylvania and others moving to hold their primaries on the first Tuesday in June.
Although Mr. Biden has built an all but insurmountable…