New polls published on Wednesday show Joseph R. Biden Jr. with a significant national lead in the Democratic presidential race as the contest heads into the intense fall campaign season, with Senators Elizabeth Warren and Bernie Sanders rounding out a threesome that seems to have separated from the rest of the primary field.
The new data, which shows Mr. Biden earning the support of about one in three Democratic voters, stands in contrast to a poll published Monday that showed a virtual three-way tie between Mr. Biden, Ms. Warren and Mr. Sanders at about 20 percent support each. On Wednesday, the director of that poll called those results an outlier.
The latest round of polling suggests that Mr. Biden’s national lead — at this early stage in the campaign — has been relatively durable throughout the summer. It has been fueled in part by the former vice president’s strong name recognition, calculations about general election viability and good will from rank-and-file Democratic voters, even as there are signs of greater volatility on the ground for Mr. Biden in the early-voting presidential primary states.
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Still, national polls can offer a snapshot of the Democratic electorate’s mood, and of the extent to which various controversies have caught the attention of voters. One of the polls published Wednesday, conducted by Quinnipiac University, showed Mr. Biden as the top choice of 32 percent of Democratic voters and independent voters who lean Democratic. Ms. Warren came in at 19 percent and Mr. Sanders was at 15 percent.
Those numbers were close to the figures Quinnipiac found at the beginning of the month, with Mr. Biden’s standing unchanged despite several weeks of scrutiny over a series of verbal gaffes.
Separately, a poll from USA Today and Suffolk University also found Mr. Biden at 32 percent, followed by Ms. Warren at 14 percent and Mr. Sanders at 12 percent.
Those numbers stand in contrast to a Monmouth University Poll that drew attention from the news media, including The New York Times, earlier in the week. It showed Mr. Biden plummeting 13 percentage points from June, putting him at 19 percent, with Ms. Warren and Mr. Sanders at 20 percent each. On Wednesday, Patrick Murray, the director of that poll, said in a statement that it was clear the results had diverged from the polling consensus.
“It occurs very infrequently, but every pollster who has been in this business a while recognizes that outliers happen,” Mr. Murray said. “This appears to be one of those instances.”
Because there is no national primary, the standing of the candidates in the early-voting primary states may matter far more than nationwide snapshots. Some surveys this summer have shown Mr. Biden’s lead in Iowa and New Hampshire ebb since he entered the race in April, and conversations with voters in Iowa have revealed signs of an enthusiasm challenge for the front-runner.
Ms. Warren and Mr. Sanders, meanwhile, have established themselves in a tier above the rest of the Democratic field. No other candidate has consistently reached double-digit support in recent surveys; in the Quinnipiac and Suffolk polls, the only other candidates with 5 percent or better were Senator Kamala Harris of California and Mayor Pete Buttigieg of South Bend, Ind. More than a dozen of the Democrats got just 1 percent — or less.
The Quinnipiac poll, conducted Aug. 21-26, and the Suffolk poll, conducted Aug. 20-25, had margins of sampling error of plus or minus five percentage points among Democratic voters. The Monmouth poll, conducted Aug. 16-20, had a margin of error of plus or minus six points. All three were conducted by telephone.
The latest round of polling also suggests that the Democratic candidates are on track to have only one presidential debate next month, after two rounds of two-night debates earlier this summer. As of Wednesday’s deadline to qualify for the September debate, only 10 candidates had done so, meaning they can all fit on one stage under the rules set by the Democratic National Committee.
The committee requires that candidates land 130,000 individual donors and 2 percent support in at least four qualifying polls in order to make the debate stage.
The billionaire impeachment activist Tom Steyer was close to meeting those benchmarks, collecting enough donors and hitting the 2 percent requirement in three polls so far. But he failed to reach 2 percent in either of the polls published Wednesday morning, leaving him one poll short as the midnight deadline approached.