(CNN) Sen. Bernie Sanders raised more than $25 million over the past three months, his campaign said Tuesday morning.

The haul -- up more than $7 million from his second quarter total -- underscored Sanders' continued strength with small dollar donors. The campaign announced last week that it had received contributions from more than a million people.

"Bernie is proud to be the only candidate running to defeat Donald Trump who is 100 percent funded by grassroots donations -- both in the primary and in the general," Sanders campaign manager Faiz Shakir said in a statement celebrating the new figures.

He also took aim at the press coverage of the campaign, which has struggled in recent early-state polling amid internal tensions over its strategy and spending.

"Media elites and professional pundits have tried repeatedly to dismiss this campaign," Shakir said, "and yet working-class Americans keep saying loudly and clearly that they want a political revolution."

The campaign in a press release said that September had been its strongest fundraising month to date.

Average third-quarter donations

Sanders spokesman Mike Casca also told CNN on Tuesday that about 130,000 people had signed up to make monthly recurring contributions and that 99.9% of its total donor base had not yet given the individual maximum of $2,800 per election -- further signs that Sanders is well-positioned to keep up his current fundraising pace.

Individuals who listed their occupation as "teacher" were the most frequent donors to Sanders, according to the campaign, which said "the three most common employers (of its contributors) were Starbucks, Amazon and Walmart."

The average donation during the third quarter, the campaign said, was $18.07. Since entering the race in February, Sanders has raised $61.5 million, according to the statement. He also transferred an additional $2.6 million to his presidential coffers from other campaign accounts during the third quarter.

On September 19, when the campaign announced that it reached the million donor mark, it highlighted contributions from voters in counties that backed former President Barack Obama in 2012 before flipping to President Donald Trump four years later. Sanders received 81,000 donations from those potentially decisive regions, the campaign said. Sanders recently concluded his "Bernie Beats Trump" tour of Iowa counties that backed Obama twice before turning to Trump three years ago.

Sanders raised $18.2 million from more than a half-million donors during the first 41 days of his campaign, nearly $6 million of it coming in on the day he entered the race. His pace slowed in the second quarter, which concluded at the end of June, but still brought in another $18 million

Polling slowdown

The impressive Sanders fundraising total comes on the heels of polling that suggests his campaign is stuck in neutral, as progressive rival Sen. Elizabeth Warren steadily gains ground on former Vice President Joe Biden. Shakir told CNN last week that the campaign was prepared to refocus its efforts to Iowa and New Hampshire, where Sanders has shown signs of fading.

Despite the acknowledgment of a strategy shift, Shakir made it clear that Sanders' travels across the country, and the campaign's investment in resources beyond the early states, were key to his ability to keep his base activated -- and giving.

"We have a support network that is nationwide and is vital to our success," Shakir said. "It is important that we remain engaged with them and that they continue to feel vested in our campaign."