Sen. Bernie Sanders' campaign manager Faiz Shakir conceded on Monday that South Bend, Indiana, Mayor Pete Buttigieg likely raised more money last quarter than the Vermont senator, but claimed the discrepancy is due to sharply different fundraising strategies of each campaign.

"I think he'll probably have more money raised than we will," Shakir told CBSN's "Red & Blue," referring to Buttigieg. "I think a lot of that has to do with the fact of how he is raising his money."

"Bernie Sanders does not go into closed-door high-dollar fundraisers and solicit money from corporate executives at their homes," he added.

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On Monday the Buttigieg campaign said it raised $24.8 million from 294,000 donors in the quarter that ended Sunday, the largest haul of any 2020 Democratic candidate to date. The average contribution was $47.42 and the campaign currently has $22.5 million cash on hand.

A Buttigieg aide said the candidate headlined 70 fundraisers in the second quarter, 20 of which were "grassroots" fundraisers. The campaign has held multiple fundraisers in cities like New York, Los Angeles, San Francisco and Chicago. On July 6, Buttigieg will headline a fundraiser at the home of businesswoman Heather Reisman and her husband, billionaire investor Gerry Schwartz, in Nantucket, according to an invitation to the event obtained by CBS News. Tickets for that event start at $250, and the campaign will hold a "grassroots" event on Martha's Vineyard soon after, with tickets beginning at $15.

Defending Sanders' fundraising efforts, Shakir said the campaign is galvanizing working-class Americans to bring about sweeping structural policies designed to "fundamentally" change America.

"For that reason, it's very hard often for us to compete with those who try to go into the homes of corporate executives," he said.

Still, Shakir said the campaign will soon demonstrate that a "massive movement" is coalescing around Sanders that will ensure that the self-described democratic socialist will again mount a formidable bid to secure the presidential nomination against the 24 other Democrats running.

He noted he expects the Sanders campaign to again receive the highest number of individual donations during the second fundraising quarter of 2019.

Jack Turman and Sarah Ewall-Wice contributed reporting.