Sen. Bernie Sanders raised $18 million for his Democratic presidential campaign in the second quarter, his campaign reported Tuesday, a number that, while shy of the high water mark set by rival South Bend, Indiana Mayor Pete Buttigieg, nonetheless showed the Vermont senator's staying power in a crowded field.

The $18 million came from "nearly 1 million donations," the Sanders campaign said in a statement announcing the numbers—at an average of around $18. Sanders transferred into his coffers an additional $6 million from other committees, the campaign said, bringing the total they reported for the second quarter to $24 million.

"The Bernie grassroots machine chugs along," tweeted BBC reporter Anthony Zurcher.

The campaign stressed the Sanders approach to raising money from grassroots, small-dollar donors and the campaign's aversion to big money power players.

"This is a movement built by working people all across this country," campaign manager Faiz Shakir said. "While other candidates court big money at fancy fundraisers, this campaign is supported by teachers, retail workers, and nurses who are putting what little money they have behind the one candidate who can bring about the transformative change this country needs."

The top 10 most common donors were employees of conglomerate retailers like Walmart, Target, and Amazon. The most common profession of donors was a teacher.

"Our strength is in numbers and we have a million person movement committed to this campaign who can give over and over again," said Shakir.

In the first quarter, Sanders raised $18.2 million. Another $18 million from donations in the second quarter, said Center for Public Integrity money in politics reporter Carrie Levine, "signals the campaign has stayed steady."

Sanders is the second presidential candidate to share fundraising numbers for the second quarter. On Monday, Buttigieg's campaign announced the mayor raised $24.8 million from 294,000 donations, an average of around $84. Shakir, in a Monday evening appearance on CBS News program "Red and Blue," acknowledged the Buttigieg number was higher than what Sanders raised but claimed that "a lot of that has to do with the fact of how [Buttigieg] is raising his money," citing the mayor's reliance on big money donations.

On Tuesday, Shakir reinforced the message of small dollar donors making the difference in the campaign.

"By rejecting the influence of corporate money we have built a campaign that not only speaks to the working people and their issues but supports them in tangible ways," said Shakir. "This is what a Bernie Sanders presidency would look like."

Sanders and Buttigieg are the first two 2020 candidates to announce fundraising numbers for the second quarter. The deadline to report is July 15.