(CNN) Sen. Bernie Sanders raised $18 million for his Democratic presidential campaign in the second quarter of 2019, his campaign announced Tuesday.

The Sanders campaign also transferred $6 million from prior campaign accounts, bringing the total amount the campaign brought in the second quarter to $24 million.

The $18 million Sanders raised from second quarter contributions falls short of the $24.8 million that South Bend, Indiana, Mayor Pete Buttigieg 's campaign announced it raised in the same period.

The haul demonstrates that Sanders continues to be able to draw millions of dollars from a large pool of small donors, a central argument of his campaign and a direct distinction between the Sanders campaign and some of his main competitors, like Buttigieg and former Vice President Joe Biden, who are raising money from high-dollar donors.

However, despite being a well-known candidate with an enormous online fundraising network built off his 2016 campaign, Sanders still fell $6 million short of Buttigieg, who up until a few months ago was a relatively unknown mayor of a mid-sized Midwestern city. Polls are also showing Sanders falling behind Sens. Kamala Harris and Elizabeth Warren, who both made significant gains in the latest CNN poll which was taken after the first Democratic debate.

The Sanders campaign expects to have $30 million on hand when they finish their report with the Federal Election Commission, which is due on July 15. The average donation to Sanders in the second quarter was $18, below his average donation of $27 in 2016.

Sanders had significant resources available to buttress the $18 million he raised during the second quarter. At the end of the first quarter of 2019, he had $8.7 million in his Senate campaign account and nearly $2.2 million left over in the account for his 2016 presidential campaign. Since the FEC allows candidates to transfer funds between comparable campaign accounts, Sanders was able to add $6 million to his second quarter haul from those reserves.

Sanders also benefits from a Netflix-style subscription model that his campaign announced in February. When the campaign announced the model, they said they brought in $600,000 from people from people who have signed up to automatically donate to his campaign each month (about $1.8 million during a 3-month period). The campaign told CNN on Tuesday that number is now $1 million a month.

Ultimately, Sanders' team says their model serves them better from a political and practical standpoint. First, they say the stark distinction of his funding coming predominately from small dollar donations instead of closed-door fundraisers is something that Democratic primary donors are yearning for.

"This money wasn't raised at a closed-door fundraiser where people are eating parmesan encrusted salmon on toothpicks," said campaign manager Faiz Shakir, in a clear shot at the pool reports from Biden's fundraisers, which often feature dispatches on the catering at the events.

Second, the campaign says the low-dollar model, which often leads to a frequency of donations over a long period of time, will sustain their efforts for the foreseeable future. Sanders campaign senior adviser Jeff Weaver said that some of the rival campaigns that raise more are cashing several $2800 checks for the maximum donation allowed under FEC rules.

"There are only so many $2800 checks to go around," Weaver said. "We don't have to raise the most money. We can do it with a little less than other campaigns. There is no concern about falling behind the other folks."

Update: This story has been updated to reflect that the Sanders campaign now brings in $1 million a month from people who signed up to automatically donate.