WASHINGTON — The swarm of Democratic contenders descending on Iowa and New Hampshire is growing so big that last week, the party issued an edict aimed at keeping the debates manageable when they start in a few months.

Only the top 20 will get invited.

That’s a lot of would-be presidents. But once voting starts, few will survive.

In 2020, candidates will have precious little time to recover from early stumbles, or to capitalize on surprise wins. Because right after Iowa, New Hampshire, South Carolina and Nevada — where retail-level politicking is at a premium — the race explodes into a massive Super Tuesday that includes the two biggest prizes, California and Texas.

That puts a premium on money and organization. And it likely means a big boost for home state favorites: Sen. Kamala Harris in California and, in Texas, Julián Castro and maybe Beto O’Rourke, too.

By the time the dust settles that Super Duper Tuesday, more than a third of all unpledged delegates will be parceled out.

Candidates who neglect the big states as they’re trudging through the snow in Manchester, N.H., and holding town halls at a Pizza Ranch in Ottumwa, Iowa, will not have time to recover.

They’ll need to round up money for ads, volunteers and staff if they have any hope of being competitive in the mega-states.

It’s a major challenge.

“You’ve got to get your campaign rolling in several places at once,” said Timothy Hagle, a University of Iowa political scientist. But “you still have to do well in Iowa.”

Texas has 20 media markets. California has 11. These states aren’t like New Hampshire, where most of the electorate is within a three-hour drive. Reaching millions of voters requires massive spending on advertising.

In 1976, Jimmy Carter, an obscure Georgia governor, went all in on Iowa and pulled off a win that catapulted him to the nomination. Could such a feat happen in 2020, given the sequence of contests?

Not likely, say the experts.

"It would take a heck of a lot of things falling into place," said Josh Putnam, a political scientist behind the authoritative Frontloading blog, which tracks rules and schedules for primaries.

1 / 6Potential 2020 Democratic presidential candidate Beto O'Rourke told reporters Friday in Madison, Wis., that he plans to make a decision soon on whether to get in the race. O'Rourke's first visit to the battleground Midwest continued Saturday with an address to the United States Hispanic Leadership Institute's national conference in Chicago.(Scott Bauer / The Associated Press) 2 / 6Sen. Bernie Sanders of Vermont greeted a supporter during a recent news conference on Capitol Hill to announce legislation to expand Social Security. Sanders' proposal would contribute to Social Security with payroll taxes on income above $250,000. On Feb. 16, news reports circulated that he had recorded a video announcing another run for president.(Mark Wilson / Getty Images) 3 / 6Sen. Elizabeth Warren, D-Mass., campaigned at the University of Iowa on Feb. 10, 2019. The visit came a day after she announced that she's running for the 2020 Democratic nomination for president. (Scott Olson / Getty Images) 4 / 6Sen. Kirsten Gillibrand, D-N.Y., shook hands with a patron while visiting a coffee shop in Concord, N.H., on Feb. 15, 2019. Gillibrand visited New Hampshire as she explores a 2020 run for president.(Charles Krupa / The Associated Press) 5 / 6Former Vice President Joe Biden spoke at The Theatre at Grand Prairie last month during his American Promise Tour.(Ryan Michalesko / Staff Photographer) 6 / 6Sen. Cory Booker, D-N.J., left a campaign event at Iowa River Brewing on Feb. 9, 2019, in Marshalltown, Iowa. Booker, who has family from Iowa, was campaigning for the 2020 Democratic nomination for president.(Scott Olson / Getty Images)

Big contests have been clustered early on the nomination calendar before. The new element for 2020 is having California and Texas, the biggest prizes, on the same day and as an added wrinkle, each with home state favorites.

“That’s going to advantage candidates who have the resources and can organize in a state like Iowa, where it’s really retail politics, shaking hands, kissing the babies — and also be able to perform adequately in the air war — to be able to throw ads up on TV across the country," Putnam said. "To be more than one place at once. That’s not something that every candidate’s going to be able to pull off.”

Our country must be defined not by our smallness, our fears, or our paranoia but by our personal stories, the courage of our convictions, and the big, bold, ambitious things we want to achieve together. pic.twitter.com/D29oEUJgke — Beto O'Rourke (@BetoORourke) February 16, 2019

As of Friday, nine major Democrats were running or had at least announced an exploratory committee, with 16 more eyeing the race.

Strategists and elections scholars don’t expect nearly that many on next year’s ballots. Some will forgo the race. Others, unable to gain traction, will drop out.

The four earliest states rarely anoint the eventual winner. They do winnow the field, though. Super Tuesday, one month after Iowa, is likely to kill off most of the rest.

In 2020, much of that churn will be taking place simultaneously: Californians can start voting by mail on Feb. 3 — the same day as the Iowa caucuses. Early voting in Texas starts a few days later.

Candidates won’t have the luxury of focusing on Iowa and New Hampshire, to the exclusion of bigger, costlier states, and have much hope to still be in the race by mid-March.

It’s a bit of a Catch-22.

“You have to develop strong infrastructure, if not in all those states, certainly in California and Texas,” said Rep. Joaquin Castro of San Antonio, who chairs his brother Julián’s presidential campaign. And “if you don't play in Iowa and New Hampshire, your money dries up.”

He conceded that in California, Harris “would have a strong leg up on everybody. But I also think that we could eat into that,” thanks to the state’s large Hispanic population. Julián Castro is the only Hispanic candidate.

“We’ll be organizing the hell out of Texas. I don’t know whether Beto’s going to run. He would obviously be formidable in Texas as well,” Joaquin Castro said.

O’Rourke raised an eye-popping $80 million in his closer-than-expected Senate race against Ted Cruz, most in small increments through the online portal ActBlue. His donor list is enviable.

He’s slipped in polls as Harris, Sens. Elizabeth Warren and Kirsten Gillibrand and others have launched campaigns. It’s widely assumed that, more than most, he could raise the sums needed to be competitive, though that may hinge on how long he waits, and whether someone like Sen. Cory Booker catches fire, or if former Vice President Joe Biden jumps in.

For Harris, there’s no guarantee that being a favorite daughter will yield victory in California. She still has to run the race.

Home state edge

But historically, the home state advantage has been huge.

Since 1976, 37 of 40 contested primaries went to a home state candidate — often in a blowout. The average margin of victory was 37 percentage points, according to David Faris, a political scientist at Roosevelt University in Chicago who has written extensively about tweaks to the political calendar.

Since 2000, the average victory margin has been 27 points.

How would that translate in the 2020 Democratic scramble?

A blowout for Harris in California — and she's already working on it — would leave her plausibly with 400 or more pledged delegates, nearly a third of the total awarded through Super Tuesday. Texas is smaller, and if O'Rourke and Castro are both in the race and split the bounty, Harris would have an even better chance at pulling far ahead of anyone else.

California alone holds more than 10 percent of the pledged delegates needed for the Democratic nomination.

It wouldn’t be long before pundits call it a two-person race, Faris speculated. In 2016, Vermont Sen. Sanders struggled to overcome perceptions that Hillary Clinton had sealed the race even when she held only a narrow lead.

But the home state advantage only accrues if you’ve done well enough in an early contest, said Steve Munisteri, a former Texas GOP chairman who has worked on a half-dozen presidential campaigns.

Otherwise it’s “a zombie campaign. ... You're really dead and you don't know it,” he said.

Early contests still critical

That’s why early contests remain pivotal, even as the one-two punch of Texas and California loom over the contest.

In 2016, Cruz lost three of the first four contests. But he’d won Iowa and that kept him alive until the race reached Texas on a Super Tuesday that, without California, wasn’t quite as momentous as the 2020 version.

“It is a tremendous advantage if you're from the state, if people think you still have a chance to win,” Munisteri said. With 20 contenders, he said, finishing in the top five is probably good enough. Otherwise, “You don't get the money. People don't take you seriously.”

There are few exceptions. In 2016, Ohio Gov. John Kasich lost 24 state GOP primaries before Ohio gave him his only win. By then, he was the only moderate still hanging on against front-runners Donald Trump and Cruz.

But when Sanders beat Clinton in New Hampshire in 2016, after she’d won in Iowa, the story lines boiled down to: “Can Hillary Clinton recover? What happened in her campaign that made it crash and burn?” recalled Andy Smith, a University of New Hampshire pollster. “That's all the people in these other states are going to be seeing, because they're not paying attention to the race.”

“Frontloading actually makes New Hampshire and Iowa more important,” not less, he argued, “because there's no time to recover. ... The dominoes fall, because the message about the candidates has already been set. You're a winner or you're a loser.”

California dreaming

California held its primaries in early March in 1996, 2000 and 2004. The legislature moved it to June to shorten the state’s election season.

But frustration simmered about holding a primary so late, it was often irrelevant. With Trump in the White House, and California a hotbed of anti-Trump resistance, the legislature moved the primary to the earliest date allowed: the first Tuesday in March.

In Democratic primaries, most pledged delegates are awarded by congressional district (Texas uses state Senate districts), with bonus delegates awarded to the top vote-getter statewide. Candidates have to get at least 15 percent of the vote in a district to collect any of its delegates.

That threshold rule may prompt some of Harris’ rivals to try to pick off a few districts here and there. But she’s a proven winner statewide. And if she carries California by the typical margin for home state favorites, she could end up with more delegates at home than the rest of the candidates combined can win that day around the country.

“She could flame out but ... it’s hard to see anyone catching Harris if she wins California decisively,” Faris said.

The flip side is that expectations are so high, Warren or someone else might see value in camping out in California for a month — not to win, but to keep Harris from overwhelming victory.

“If you don’t do as well as expected in your home state, it’s a crushing blow,” Faris said. “You’d have to be strategic about it.”