Sen. Bernie Sanders, who has been slipping in the polls, ​announced on Tuesday that his campaign raised more than $25 million in the last three months from more than a million contributors.

Sanders, who has fallen behind former Vice President Joe Biden and Sen. Elizabeth Warren, ​got $25.3 million from 1.4 million donations, his campaign said.

The third-quarter haul was the Vermont senator’s most successful fundraising effort of the 2020 campaign.

He took in about $18 million in each of the first two quarters.

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

Pete Buttigieg’s campaign said the mayor of South Bend, Ind., raised m​ore than $19.1 million in the quarter, a decline from the $24.8 million his campaign amassed during the second quarter.

“We will have the resources to go the full distance, and to win, the 2020 nominating contests,” said his campaign manager, Mike Schmuhl.

Candidates have until Oct. 15 to file their third-quarter fundraising totals with the Federal Election Commission.

With Post wires