Candidates with the most individual donors Darker shades on the map indicate a greater share of estimated donors. 1. Sanders 746,000 1. Sanders 746,000 2. Warren 421,000 2. Warren 421,000 3. Buttigieg 390,000 3. Buttigieg 390,000 4. Harris 277,000 4. Harris 277,000 5. Biden 256,000 5. Biden 256,000 6. O’Rourke 188,000 6. O’Rourke 188,000

Note: Data is through June 30.

Senator Bernie Sanders of Vermont has a huge lead over other Democratic presidential candidates in the number of individual donors they have each accumulated so far.

This is the first time since the primary race began in earnest that we can estimate how many individual donors each candidate has attracted — a key indicator of how much they are catching on with voters.

Mr. Sanders is relying heavily on small donors to power his campaign, and he entered the 2020 race with a huge network of online donors who supported his 2016 presidential bid. The map above shows the breadth of Mr. Sanders’s roster of donors across the United States.

A map that includes the rest of the Democratic field without Mr. Sanders offers a picture of where the other major candidates are picking up donors. Senator Elizabeth Warren of Massachusetts, the other leading progressive in the race, is outpacing the rest of the field across much of the country — a sign that her strategy of relying on grass-roots donors, and refraining from holding high-dollar fund-raisers, is working.

Candidates with the most individual donors when Sanders is excluded Where Bernie Sanders is leading, the runner-up is shown. Darker shades on the map indicate a greater share of estimated donors. 1. Sanders 746,000 1. Sanders 746,000 2. Warren 421,000 2. Warren 421,000 3. Buttigieg 390,000 3. Buttigieg 390,000 4. Harris 277,000 4. Harris 277,000 5. Biden 256,000 5. Biden 256,000 6. O’Rourke 188,000 6. O’Rourke 188,000

The map also shows regional strength for some candidates, like former Vice President Joseph R. Biden Jr., who is doing well in Delaware and northeastern Pennsylvania, as well as in many places across the Southeast. Senator Kamala Harris of California is formidable in her home state, the nation’s most populous. And Mayor Pete Buttigieg of South Bend, Ind., has drawn strong support in some parts of the Midwest.

Attracting individual donors has been particularly important in the 2020 race because the Democratic National Committee is using grass-roots fund-raising as one of the qualification standards for the debates. To qualify for the next round of debates in September, candidates will need to have at least 130,000 unique donors, in addition to meeting a polling requirement.

[See which Democrats are leading the 2020 presidential race.]

While the campaigns have been required to reveal their overall fund-raising totals, and many have released information about their number of donors, it has not been possible until now to estimate how many donors each Democratic candidate has attracted.

Our analysis is based in part on fund-raising records disclosed on Wednesday by ActBlue, an online fund-raising platform that processes donations for the Democratic candidates.

While the number of donors is especially important in the 2020 primary race, the amount of money that campaigns raise is ultimately what allows them to pay the bills. By that measure as well, Mr. Sanders leads in large parts of the country.

Candidates who have raised the most money Darker shades on the map indicate a greater share of money raised. 1. Sanders $36 million 1. Sanders $36 million 2. Buttigieg $32 million 2. Buttigieg $32 million 3. Warren $25 million 3. Warren $25 million 4. Harris $24 million 4. Harris $24 million 5. Biden $22 million 5. Biden $22 million 6. O’Rourke $13 million 6. O’Rourke $13 million

Over all, Mr. Sanders is leading his rivals in total money raised, but not by a huge margin — even though he has far more donors than any of them.

Most other candidates are drawing in more dollars per donor — an estimated average of roughly $80 for both Mr. Biden and Ms. Harris, for example. Mr. Sanders, on the other hand, has brought in an estimated $46 per donor.

Mr. Sanders’s campaign has tried to encourage larger contributions. “We have two choices: We need more donations or we need people to give just a bit more than they have before,” Faiz Shakir, Mr. Sanders’s campaign manager, wrote in an email in the spring.

While Mr. Sanders has a sprawling list of donors nationwide, geographic dominance does not necessarily translate into a cash advantage of the same magnitude. Just as population density differs in urban, suburban and rural areas, the number of people who donate to political campaigns also varies widely based on geography.

Ranking as the top Democrat for individual donors in a densely populated urban area is far different from leading the field in an area where few people are donating to campaigns.

For example, Ms. Warren has more donors in a single ZIP code in Brooklyn than any candidate has in the entire state of Mississippi. Mr. Buttigieg has more donors in a single ZIP code in Washington, D.C., than any candidate has in South Dakota.

Here’s a look at who has the largest number of individual donors in some major metropolitan areas.

New York City Buttigieg Sanders Warren New York City Buttigieg Sanders Warren Sanders Boston Buttigieg Warren Sanders Boston Buttigieg Warren Warren Washington, D.C. Harris Buttigieg Biden Warren Washington, D.C. Harris Buttigieg Biden Buttigieg Chicago Sanders Buttigieg Chicago Sanders Sanders Buttigieg Warren Harris Atlanta Biden Sanders Buttigieg Warren Harris Atlanta Biden San Francisco Warren Buttigieg Oakland Sanders Harris San Francisco Warren Buttigieg Oakland Sanders Harris

Many Democratic candidates have struggled so far to develop a broad donor base across the nation, though in some cases they at least have bragging rights in their own backyard. Senator Amy Klobuchar of Minnesota has the largest number of donors in most of her state, as does Gov. Steve Bullock of Montana in his state.

Former Representative Beto O’Rourke of Texas, whose fund-raising slowed significantly after a strong start, leads the field in donors in most of his state.