Many potential Democratic presidential candidates will spend the last few weeks of this year consulting with colleagues, supporters and family members as they decide whether to announce, in January or soon thereafter, that they will seek their party’s presidential nomination in 2020.
The first delegate selection events of 2020 will take place roughly 14 months from now, with the Iowa caucuses planned for Feb. 3 and the New Hampshire primary tentatively scheduled for Feb. 11.
The dates for the next Democratic National Convention have also been set: July 13 through 16, 2020. The Democratic National Committee will choose the site for the convention in the next few months. The finalist cities are Houston, Miami and Milwaukee. If the DNC ranks the states in which these cities are located by the competitiveness and size of their electoral votes, Miami would be the most likely convention site, followed by Milwaukee and Houston.
While not all the rules for the 2020 Democratic Convention have been set, one important change has already been approved that will make the 2020 convention different from its predecessors. This change involves the role of superdelegates: the ex-officio positions held by members of the U.S. House and Senate, governors, other officeholders and members of the national and state Democratic committees.
In 2016, superdelegates made up about 15 percent of all delegates to the convention, and nearly 30 percent of the number of delegates needed to win the nomination. Sen. Bernie Sanders was very critical of the superdelegate system, saying it permitted unelected delegates, most of whom supported Hillary Clinton’s presidential candidacy, to have an outsize influence at the 2016 convention.
The number of Democratic superdelegates will be reduced by about 60 percent from 2016 to 2020. In practice, this means that there will be far fewer state and national party committee members serving as ex-officio delegates. Nearly all Democratic members of the U.S. House and U.S. Senate, and nearly all the Democratic governors, will continue to be convention delegates.
More importantly, the superdelegates will not be allowed to vote on the first ballot at the convention if their votes would make a difference to the outcome. In other words, if a candidate has accumulated enough votes in the primaries and caucuses to have a majority of the elected delegates on the first ballot, that candidate will be nominated, regardless of the views of the superdelegates.
The only circumstance in which superdelegates could vote on the presidential nominee at the convention would be if no candidate had enough primary or caucus delegates to win a first ballot majority. In that case, superdelegates could vote on the second and subsequent ballots. 
The last Democratic convention to go to a second ballot was in 1952. With the rise of primaries and caucuses as delegate selection events since the 1970s, the eventual nominee has always won a clear majority of the delegates by the time the last primary was held in June.
The final calendar of 2020 Democratic primaries and caucuses has yet to be established. The four states that traditionally go first — Iowa, New Hampshire, South Carolina and Nevada — will almost certainly continue to select their delegates in February. 
However, many other states, particularly larger ones, may move their primaries up to early- to mid-March from later in the spring. California Gov. Jerry Brown has already signed a bill to hold that state’s primary on March 3, 2020, the earliest day states other than the “first four” may elect delegates.
Rescheduling the California primary from June to March could have significant impacts on how candidates allocate their time and money in early 2020. An earlier California primary also means that candidates will need to declare earlier, so they can begin to organize a staff and mobilize voters in the nation’s largest state.
Eric L. Davis is professor emeritus of political science at Middlebury College.