WASHINGTON — Pulling almost even with Hillary Clinton in Iowa produced a huge financial windfall for Bernie Sanders.

The Vermont senator’s campaign raised $3 million after his narrow second-place finish in the Iowa Democratic caucuses — the best fund-raising day ever for Sanders’ campaign.

“I’ve been overwhelmed,” Sanders told CNN Wednesday about the number of individual campaign contributions.

“That indicates to me not only the kind of grass-roots support we have, but that also tells me people . . . are sick and tired of ­super PACs . . . and billionaires buying elections.”

Overall, Sanders netted $73.5 million in individual contributions last year — 74 percent of that from people giving less than $200.

Sanders, a self-described socialist, has been hammering at Clinton for taking speaking fees and donations from Wall Street, and has assailed the millions her super PAC has collected from wealthy supporters.

“I do not know any progressive who has a super PAC and takes $15 million from Wall Street,” Sanders said during CNN’s Democratic presidential town hall in New Hampshire Wednesday night.

Clinton, meanwhile, spent the town hall defending the $675,000 in speaking fees she accepted from Goldman Sachs.

“That’s what they offered,” Clinton said when asked why she took the money.