Nothing is yet final, but over all less than 5 percent of pledged delegates are set to be awarded by caucuses in the Democratic primary, down from 14 percent in 2016. About a third of those delegates will be decided by minor overseas contests in U.S. territories, like Guam and the Virgin Islands.

The remaining caucus states are also adopting rule changes that tend to increase turnout, like absentee or even online voting. It is hard to know how much these will dent the traditional advantages of candidates further to the left, but Mrs. Clinton was also stronger in higher-turnout caucus elections in 2016, winning key early races in Iowa (narrowly) and Nevada.

How much will it matter in 2020? Could it help an establishment-backed politician like Joe Biden if he joins the race?

The overall effect seems as if it will be pretty modest.

That might be something of a surprise. After all, the effect of having a caucus is substantial. In the last two Democratic primaries, Mrs. Clinton fared about a net 20 points worse in caucuses than primaries, even after controlling for their demographic characteristics.

In 2008, Texas had both a Democratic caucus and a primary, with the caucus awarding one-third of the state’s delegates and the primary awarding the rest. Mrs. Clinton won the Texas primary by 3.5 points, keeping her in the race, but she lost the Texas caucus by 12.5 points on the same day. As a result, Barack Obama, the insurgent candidate, won the most delegates from the state.

Despite the seemingly small overall effect, you could imagine that a state victory in 2020 caused by the switch could lift a campaign for a period, affecting public perceptions and the tenor of news coverage.

Still, caucuses were worth only a net three percentage points over all to Mr. Sanders (in 2016) and to Mr. Obama (2008) in the pledged delegate count (around a 20-point margin on 14 percent of delegates in each case).