If Monday weren't Iowa Caucus Day, it would be Presidential Fundraising Day. Reports were due at midnight for the fourth quarter of 2015 for the candidates and for the second half of the year for super PACs.

While we have almost daily polls to tell us how each contender is doing in the horse race, this is our first look in a very long time at the financial health of each of them. And that's arguably just as important, because most campaigns fold due to a lack of funds -- not just a lack of traction.

So who made the biggest splash in the newest fundraising reports? Below are our winners and losers. (And make sure to check out all the highlights from The Post's Matea Gold, Anu Narayanswamy and Tom Hamburger.)

WINNERS

Bernie Sanders: The independent Vermont senator's $33.6 million raised in the fourth quarter was hugely impressive -- especially compared to front-running Hillary Clinton's $37 million. What's more impressive, though, is the fact that Sanders Camp has also announced it raised $20 million in January alone, a significant ramping up of fundraising just as we begin the actual voting process. Sanders is also doing it with a far different and much-wider pool of donors, with more than 1.3 million individual donors so far (most which can still give him more money, we would note) and an average donation of just $27.

Hillary Clinton: So, it's kind of a cop-out to include both Sanders and Clinton here. But both are more than worthy. Clinton's $37 million raised in the fourth quarter beat the previous quarter and helped her set a new record for off-year, fourth-quarter fundraising by a non-incumbent. Clinton also benefits from the more than $25 million raised in the second half of 2015 by her top super PAC, Priorities USA Action. Priorities USA Action had more than $35 million cash on hand at the end of the year. Combined with the $10 million edge in cash on hand Clinton had on Sanders -- $37.9 million to $28 million -- that means the pro-Clinton effort remains significantly more flush with cash than Team Sanders.

Ben Carson: The fourth-quarter included the short-lived Carson boomlet, which the retired pediatric neurosurgeon used to great fundraising effect. He pulled in more than $22 million, which was tops among all Republican candidates. This is a list of winners, and Carson won the GOP money race. Unfortunately for him, his momentum has completely seized, his campaign is in a state of disarray after staff departures, and he retains just $6.6 million of the $54 million he's raised thanks to heavy spending.

Ted Cruz: Cruz was second behind Carson, raising $20.5 million. He's also got the most flush campaign kitty among all GOP candidates, with $18.7 million cash on hand. And he has a network of super PACs which have spent more than $10 million on his behalf so far. For a guy whose campaign is on the rise, so is his fundraising.

Donald Trump: No, Trump didn't raise gobs of money. But he doesn't have to. And his media-focused campaign continues to be one of the most cost-effective efforts in political history. Trump raised $2.7 million from contributions and self-funded and loaned his campaign another $10.9 million in the fourth quarter. He spent just $6.9 million, which is less than four other Republicans. And yet, he remains in the lead. The question from here is how much he self-funds as the map expands beyond the small, early states -- or if he keeps focusing on winning with "earned" media. That $10.9 million investment suggests he's ready to start spending.

LOSERS

Jeb Bush: How the mighty have fallen. Bush's campaign fell behind Carson, Cruz and Sen. Marco Rubio (R-Fla.) in the fourth quarter, after placing second behind Carson in the third quarter. The $7 million Bush raised was about half of what he pulled in in the preceding three months. Perhaps more troubling for Bush, though, is the decline of his super PAC, Right to Rise. It raised more than $100 million in the first half of 2015, but it pulled in just $15.1 million in the second half. It also spent heavily but couldn't do anything to arrest Bush's polling decline. The PAC did have $59 million in the bank at the start of the year -- no small amount, to be sure. But it has spent at least $16 million so far this month. And again, none of that money has made a difference so far.

Chris Christie: The New Jersey governor's campaign still has a pulse in New Hampshire, but it doesn't have much money. It raised just $2.9 million in the fourth quarter -- a downtick from the third quarter -- and has just $1.1 million cash on hand. That's less cash and Rand Paul, Carly Fiorina and John Kasich, each of whom appear to have less hope than Christie to actually win the nomination.

Rand Paul, Mike Huckabee and Rick Santorum: This group includes two Iowa caucus winners and a guy who was initially hailed as a top contender for the White House. None of them is a factor right now though, and thus we're lumping all of them together. Huckabee and Santorum raised less than $1 million apiece and have almost no cash. Paul, meanwhile, pulled in $2 million and has just $1.3 million cash on hand. Combined with each of their falling off the debate stage in recent weeks (Paul was back on Thursday), that paints a dim picture for all three.

Super PACs: According to a review by Bloomberg, GOP super PACs raised only about 27 percent of all the money raised for 2016 candidates in the second half of 2015 -- down from 78 percent in the first half of the year. That's in large part because of the decline of Bush's super PAC, Right to Rise, but it's also interesting that we have yet to see gobs of million-dollar contributions going to the likes of Cruz and Rubio. The super PACs of both are doing okay, but they're still being far outraised by the campaigns. There has long been a sense that super PACs would take over many of the duties that campaigns traditionally have done in 2016. Despite not being able to coordinate with the campaigns themselves, their ability to raise money without contributions limits makes them an invaluable piece of the puzzle. But for now, that takeover is still a work-in-progress.