LOS ANGELES — On the day before in-person early voting was to begin across California’s most populous county, there was no sign of life at Joseph R. Biden Jr.’s campaign office in East Los Angeles last Friday. A metal gate out front was padlocked shut, with a missed-delivery notice from the Postal Service wedged into it.
In a strip mall a mile away, a campaign office for Senator Bernie Sanders was humming with activity. Field organizers were busy calling supporters, and every so often the ding of a bell signaled that another volunteer was on board.
Mr. Biden is counting on a win in the South Carolina primary on Saturday to help position him as the leading moderate challenger to Mr. Sanders, after three straight losses shredded Mr. Biden’s status as the onetime front-runner. But even if he succeeds in South Carolina, his lack of resources and thin campaign organization in California and other states that vote next week on Super Tuesday present a daunting challenge to a candidacy already on precarious footing.
Interviews with party leaders in half a dozen Super Tuesday states suggest that the same vulnerabilities that plagued Mr. Biden beginning in Iowa — subpar organization, limited outreach to local Democrats and a late start to campaigning — are holding him back in the states that next week will dole out a third of the total delegates in the Democratic primary.
Mr. Biden’s on-the-ground operations, these Democrats said, are easily dwarfed by those of Mr. Sanders and Michael R. Bloomberg, the moderate former mayor of New York who has plainly cut into Mr. Biden’s standing in some of these states even as he faces his own mounting challenges in the race.
“Arkansas was, in my opinion, going to be a default Biden state,” said Michael John Gray, the chairman of the Democratic Party of Arkansas. “He hasn’t been here. Of all the campaigns, the least organized in Arkansas is Biden.”
Other candidates, like Mr. Sanders, of Vermont, are already campaigning in Super Tuesday states, holding events that excite supporters and generate news media coverage. But Mr. Biden has planted himself elsewhere, after his fourth-place finish in Iowa and fifth-place New Hampshire result threw even his expected firewall of South Carolina into doubt.
He devoted last week to Nevada, where he pulled off the second-place finish that he was aiming for, and this week he is scheduled to be in South Carolina every day before Saturday’s primary, which he says he will win. Aside from fund-raising, he has not campaigned in a Super Tuesday state in over a month.
After the disastrous first two contests, the Biden campaign also moved staff members from Super Tuesday states to Nevada and South Carolina to provide extra manpower there.
“Bernie has a ground game because he naturally has a ground game; his whole campaign is a grass-roots campaign,” said Gilberto Hinojosa, the Democratic Party chairman in Texas, the second-biggest delegate prize on the Super Tuesday map. “Bloomberg has funded a ground game. Elizabeth Warren has a ground game because she started organizing in Texas a long time ago.”
As for Mr. Biden, he said, “I haven’t seen anything other than the events he’s had in Texas.”
Certainly, Mr. Biden has a long list of congressional endorsers. He enjoys widespread name recognition and a reservoir of good will within the party. His rivals have many vulnerabilities that are increasingly being litigated in the national spotlight, and a decisive victory in South Carolina, his allies hope, could catapult him into a strong showing on Tuesday.
On Wednesday, he picked up the endorsement of Representative James E. Clyburn of South Carolina, the most influential Democrat in the state, giving him another boost in the final days.
Yet a number of Democratic state chairs and other party leaders said in the last week that outreach from Mr. Biden continued to be light. Some said they had not heard from Mr. Biden personally — a contrast with Mr. Bloomberg — and Mary Mancini, the chairwoman of the Tennessee Democratic Party, said on Monday she had not heard from Mr. Biden’s senior staff, either. She said that Mr. Biden had a “natural constituency” in the state, but added, “Biden might be taking those voters for granted.”
Anthony Daniels, the state House minority leader in Alabama, said, “Whoever was guarding the hen house in Alabama obviously didn’t do their job in making sure a certain level of engagement was where it needed to be.”
One of Mr. Biden’s biggest problems is that he is sorely outmatched when it comes to money: He entered February with just over $7 million on hand, less than half of what Mr. Sanders had, and he cannot keep pace with Mr. Bloomberg and another billionaire in the race, Tom Steyer.
That financial disadvantage has ramifications both for television advertising and for staffing: Multiple North Carolina Democrats, for example, said they knew of only one Biden campaign staff member in the state. Mr. Bloomberg’s campaign, by comparison, said it had more than 125 staff members there. The Biden team said it had a staff “in the double digits” in North Carolina.
In California, Mr. Bloomberg has 24 offices and more than 300 staff members, while Mr. Sanders has 23 offices and just over 100 staff members, according to their campaigns. The Biden office in East Los Angeles is the only one in the state, and his campaign declined to say how many staff members it had on the ground.
“Could he do more if he had more money? Absolutely,” said Hilda L. Solis, a Biden supporter who served as labor secretary during President Barack Obama’s administration and is now a Los Angeles County supervisor. But she noted that Mr. Biden enjoys the advantage of already being widely known.
Mr. Biden has also been conspicuously absent from the airwaves in Super Tuesday states. In comparison, Mr. Bloomberg has spent $183 million on television ads in those states, Mr. Steyer has spent $35 million and Mr. Sanders has spent $13 million, according to Advertising Analytics, an ad tracking firm.
“It’s to the point where you can ask a 14-year-old who’s running for president, they’re going to say ‘Bloomberg,’” said Mr. Gray, the Arkansas Democratic chairman.
Even one of Mr. Biden’s national co-chairs, Mayor Eric Garcetti of Los Angeles, has taken notice of the onslaught of Bloomberg ads. “I don’t think there’s a game I can play on my phone or a clip I can watch without there being an ad not just from him but from Tom Steyer as well,” he told reporters while campaigning for Mr. Biden this month in Nevada.
“That said, there’s a deeper connection that’s more emotional about Joe Biden,” Mr. Garcetti added. “That’s worth in itself millions and millions of dollars.”
In next week’s contests, Mr. Biden’s team is focusing on congressional districts that play to his strengths, and where many other candidates are likely to struggle to reach the 15 percent threshold to receive delegates.
The Biden campaign is hoping for particularly strong performances in districts with many voters of color, like Alabama’s Seventh Congressional District, a majority black district represented in the House by Terri A. Sewell, and North Carolina’s First Congressional District, which also has a large black population and is represented by G.K. Butterfield.
Both Ms. Sewell and Mr. Butterfield have endorsed Mr. Biden.
In California, in addition to Mr. Garcetti and Ms. Solis, his supporters include Senator Dianne Feinstein, the mayors of Sacramento and Long Beach, and several members of the state’s congressional delegation.
But an impressive list of endorsements does not necessarily translate into votes, as was apparent in Iowa, where Mr. Biden had the backing of former Gov. Tom Vilsack as well as two of the state’s three Democratic House members and yet still performed poorly.
Mr. Biden’s East Los Angeles office, located in a county with a population exceeding 10 million, was only barely more active during a return visit over the weekend. The padlocked gate was eventually unlocked, but when an event for volunteers got underway on Saturday, only a handful of people had shown up.
Inside the campaign office, seven large round tables were surrounded by chairs, and it was not hard to get a seat. There were fewer people making phone calls than there were tables.
Thomas Kaplan reported from Los Angeles, and Katie Glueck from Charleston, S.C.