Former Secretary of State Hillary Rodham Clinton has a 41-point lead on Sen. Bernie Sanders of Vermont in the early state of Iowa, according to a Monmouth University poll released Tuesday on the 2016 Democratic presidential field.

Mrs. Clinton had the support of 65 percent of likely Democratic caucus-goers in the survey taken from Oct. 22-25. Mrs. Clinton appeared before the House Select Committee on Benghazi on Oct. 22, and Vice President Joseph R. Biden announced a day earlier he would not enter the 2016 race.

Mr. Sanders was at 24 percent, followed by former Maryland Gov. Martin O’Malley at 5 percent and Harvard Law Professor Lawrence Lessig at 1 percent.

“We now have a two-person race, but one of those competitors has just pulled very far ahead,” said Patrick Murray, director of the independent Monmouth University Polling Institute in West Long Branch, NJ.

Mrs. Clinton had large advantages over Mr. Sanders among both men (55 percent to 33 percent) and women (73 percent to 16 percent), and had leads among “very liberal” voters (57 percent to 34 percent), “somewhat liberal” voters (68 percent to 22 percent), and moderates (69 percent to 19 percent).

Mrs. Clinton had an 88 percent favorability rating, compared to an 8 percent unfavorable rating. Mr. Sanders had a 77 percent/11 percent favorable/unfavorable split and Mr. O’Malley had a 50 percent/14 percent split. Three-quarters of respondents said they didn’t know enough about Mr. Lessig to form an opinion.

Four-in-10 Democrats say they’re completely settled on a candidate, while another 37 percent have a strong preference but are willing to consider others. Ten percent have a slight preference and 13 percent are largely undecided.

Among Clinton supporters, 49 percent are completely decided and 35 percent have a strong preference, with 16 percent looking at other candidates. Among Sanders supporters, 27 percent are completely decided, with 47 percent having a strong preference and 24 percent looking at other candidates.

Among Clinton supporters, 59 percent said Mr. Sanders would be their second choice and 14 percent said it would be Mr. O’Malley.

Two-thirds of Sanders supporters, meanwhile, said Mrs. Clinton would be their second choice and 19 percent said Mr. O’Malley would be.