SAN FRANCISCO — For more than three decades, Democrats have headed into each of their national conventions knowing exactly whom they will nominate for president, making the events little more than made-for-TV pep rallies.

But in the bar and hallways of a meeting here last week of the Democratic National Committee, some party insiders quietly expressed concern that the large field of 2020 candidates, new party rules and a front-loaded primary calendar could conspire to create a chaotic nominating convention next year.

"Unless something cataclysmic happens, I think we're looking at a contested convention," said Jim Zogby, a longtime DNC member and former member of the party's executive committee. "I think we're not going to get to the convention with an outright winner."

All the top campaigns are taking the possibility of a contested convention seriously and have begun wooing the party's 700-plus super delegates, who thanks to a new rule will only get to weigh in on a nominee if next year's primaries and caucuses fail to produce a clear winner.

On the sidelines of the DNC meeting, senior campaign aides charged with hunting for delegates could be seen stalking the halls and schmoozing with super delegates into the wee hours of the mornings, keeping close track of lists of people they wanted to connect with in person. Behind the scenes, candidates have been making calls to super delegates for months and took time at the meeting to make the rounds to gatherings of delegates.

Speculation about contested conventions —when no candidate has secured the nomination heading into the event — bubbles up every four years among political junkies, only to inevitably fizzle out. Some party insiders have fretted for months that the Democratic primaries could devolve into a 'lord of the flies' situation.

The last time Democrats went into their convention without a presumptive nominee already having a majority of delegates was 1984. And you have to go all the way back to 1952 to find the last time it took multiple rounds of ballots to pick the standardbearer.

But this time, it might happen again, according to many of the nearly two dozen state party chairs, DNC members, campaign delegate counters and other officials surveyed here by NBC News, most of whom did not want to speak for the record about the sensitive subject.

"It's more likely than not that there's going to be a brokered convention so those candidates that are really paying attention treated the DNC summer meeting like speed dating trying to make as many touches as possible with one-on-one meetings, speeches at caucuses and delegation meetings trying to lock in support from party activists and leaders," said a campaign aide involved in delegate-hunting operations who spoke on condition of anonymity.

Still, plenty of Democrats here dismissed the doomsaying and predicted a nominee would emerge early next year. Others noted that DNC members have an interest in stoking speculation, since it would put them in the catbird seat of being courted by candidates.

"This seems to be a narrative during every contested primary, but if recent history tells us anything, we feel confident that our party will come together and support whoever the eventual Democratic nominee is," said Patrice Taylor, the DNC's director of party affairs. "Our party understands that Donald Trump is a huge threat to our country, and our party’s entire goal is to be united in the effort to beat him."

But almost everyone agreed candidates were better off preparing for anything.

"Who the f--- knows?" said Harold Ickes, a former Bill Clinton aide and veteran of decades of DNC intrigue, who was the basis of a character Joe Klein's 1996 novel "Primary Colors." "But any candidate that ignores the automatic delegates (super delegates) does so at their own peril."

Super delegates can vote for whomever they want, unlike pledged delegates who have to reflect the will of voters in their states. Under the new rule, super delegates will only vote at the Democratic National Convention in Milwaukee next year if no candidate is able to secure a majority of the pledged delegates in an initial tally and a second round of balloting is needed.

The rule was intended to decrease the power of super delegates, but could turn them into tiebreakers if the pledged delegates are split among multiple candidates.

"There's a real chance this could be a brokered convention and no one has the nomination locked up heading into Milwaukee," said Kelly Dietrich, a longtime Democratic operative. "We could have four different winners of the first four primary and caucus states. People need to start thinking about it and preparing."

While there are some differences between a "brokered," "contested" and "open" convention, the terms are often used interchangeably. The key factor in all is that the outcome of the convention is not pre-determined going in.

One former top DNC official who currently serves in elective office put the odds at "just shy of 50 percent" of super delegates needing to step in if the race looks anything like it does right now by the time voters start casting ballots.

A handful of factors have converged this year to make a contested convention seem more likely.

Democrats have the largest presidential primary field in history, no prohibitive frontrunner and multiple candidates with robust small-dollar fundraising networks, meaning several could choose to stay in the race for long-haul.

Past contests, most recently in 2008 and 2016, quickly settled into two-person races. But a race of three or more makes it more difficult for any one candidate to secure a majority of the delegates.

"The '2020' election doesn't stand for the year — it stands for the number of people that are running," quipped Sen. Cory Booker, D-N.J., on Friday to DNC delegates.

Meanwhile, some of the biggest and most delegate-rich states in the country, including California and Texas, moved up their primaries on the calendar and will vote just one month after first-in-the-nation Iowa, potentially splitting their hundreds of delegates among multiple candidates in a yet-to-settle field.

In the past, California was one of the last states to vote, when it served to essentially end the primary season and ratify the frontrunner by flooding them with hundreds of additional delegates.

While Republican primaries are winner-take-all, Democrats' are not. Any candidate who gets at least 15 percent of the vote can earn delegates from a primary or caucus, so its not uncommon for candidates to split each state's delegate haul.

Some worry that the first four states (Iowa, New Hampshire, Nevada and South Carolina) will deliver a split decision, and California and other Super Tuesday states will fracture, giving multiple candidates a reason to stay in the contest and the money to do so, thanks to energized grassroots donors.

Of course, it's entirely possible someone will dominate the early primary and caucus states next year. Then front-loaded California and Texas could double down on that candidate and a presumptive nominee could emerge even earlier than in the past.

Weaker candidates would also likely face enormous pressure to drop out before the convention so the party can rally around a leader and prepare to challenge President Donald Trump.

Still, campaigns are preparing.

"It's very real," said an aide to one top campaign of the need to court super delegates.

Biden skipped the DNC meeting, but his campaign manager, Greg Schultz, hosted a private briefing for DNC members Thursday where he touted the former vice president's party-building efforts.

One of the first things billionaire Tom Steyer did after entering the 2020 race this summer was task aides reach out to every super delegate in the party to establish a line of communication.

Pete Buttigieg, the mayor of South Bend, Indiana, also skipped the DNC meeting and sent his husband instead. But Buttigieg may have spent more time speaking one-on-one with DNC members than any other candidate in the field thanks to his run for party chair in 2017. Several DNC members here said they didn't mind his absence because they already have his cell phone number.

Several campaigns also have super delegates on their staff and many rushed to snap up operatives known for understanding the party's byzantine delegate rules.

It's impossible to game out how a convention fight would play out, but some suggested Biden would have a natural advantage, given his long ties to party insiders. Others speculated about deals between like-minded candidates such as Sens. Elizabeth Warren, D-Mass., and Bernie Sanders, I-Vt.