As the coronavirus pandemic upends the presidential campaign, states across the country are postponing primary elections and expanding vote by mail options, citing the difficulty of holding elections during the outbreak.

Fifteen states and one territory — Alaska, Connecticut, Delaware, Georgia, Hawaii, Indiana, Kentucky, Louisiana, Maryland, New York, Ohio, Pennsylvania, Rhode Island, West Virginia, Wyoming and Puerto Rico — have either pushed back their presidential primaries or switched to voting by mail with extended deadlines.

Six of those states have moved their primaries to June 2, which has unexpectedly become a major date on the Democratic primary calendar. It is among the last dates available before the June 9 deadline set by the Democratic National Committee for states to hold their nominating contests.

In New York, officials delayed the presidential primary even further, to June 23. Wisconsin is holding firm to the April 7 date for its primary, but a federal judge extended absentee voting deadlines.

Tom Perez, the D.N.C. chairman, has urged states with upcoming contests to expand their use of voting by mail, no-excuse absentee voting, curbside ballot drop-offs and early voting. The committee also rescheduled the party’s national convention, from mid-July to mid-August.

Here’s a running update of major changes in an election transformed, including rescheduled primaries and caucuses and a few other key races. You can also track our full primary election calendar.