When 2015 began, few would have expected that a "democratic socialist" could seriously compete on fundraising with Hillary Clinton, the near-unanimous choice of the Democratic Party establishment.

But that's just what Bernie Sanders has managed to do.

The Vermont senator's campaign announced on Saturday that he had raised $33.2 million in the most recent fundraising period — and $73 million for his campaign overall. This is a huge sum that ensures that his campaign won't lack for cash as the first caucuses and primaries near.

Now, Hillary Clinton did raise a good deal more than Sanders overall ($112 million to $72.8 million). But she's already spent a ton of the money she brought in — as you can see here, the $38 million she has left in the bank (her "cash on hand") isn't all that much higher than Sanders's $28.4 million.

And Sanders's Q4 fundraising (money raised in the last three months of 2015) is really close to Clinton's (she raised $37 million compared with his $33.2 million).

Sanders's achievement is all the more impressive both because he doesn't have access to the traditional Democratic fundraising networks (indeed, he's been warring with the party establishment), and because of his constant criticism of the influence of corporations and the superrich.

Instead, he's shown just how incredibly powerful small-donor fundraising can be. According to totals released by Sanders's campaign, they got donations from more than 1 million people in 2015 — and 99.9 percent of those people can give again, because they haven't yet hit the $2,700 fundraising maximum for a primary election donation from an individual.

It also seems near certain that Sanders's fourth quarter total of $33 million raised will be higher than any Republican candidate in the race. Though few Republicans have disclosed their most recent fundraising numbers yet (they have until January 15 to do so), Ben Carson and Ted Cruz, thought to be the two top GOP fundraisers in traditional campaign dollars, raised $23 million and $20 million in the fourth quarter, respectively — well behind Sanders. But of course, these GOP candidates (and Clinton) will be aided by outside Super PACs that can raise unlimited amounts.