The survey, which was conducted this past Monday through Thursday and released just nine days before the caucuses, highlights the pressure on Sanders’ rivals, who have seen the independent senator from Vermont surge in the weeks leading up to the first votes of the Democratic nominating process. A Des Moines Register/CNN/Mediacom poll released two weeks ago also showed Sanders with a single-digit advantage in the caucuses, though Biden has led in other surveys released since that.

After Iowa, Sanders also leads in polls of the first-in-the-nation primary in New Hampshire —and victories in both of the earliest voting states would make him the favorite to capture the party’s nomination.

In Iowa, the poll shows, Sanders is driven by support among young voters — along with a sizable gender gap.

Among the youngest voters — those under 30 — Sanders is the first choice of 40 percent, leading Buttigieg (16 percent), Warren (16 percent) and Biden (10 percent).

Biden, meanwhile, is the top choice of 32 percent of Democrats 65 and older, with Buttigieg (17 percent), Klobuchar (13 percent), Sanders (9 percent) and Warren (8 percent) trailing behind.

Roughly one-in-three male Democrats, 34 percent, say Sanders is their first choice — giving him a nearly 20-point lead among men over Buttigieg (15 percent), Biden (14 percent) and Warren (10 percent). The race is essentially tied among women, however, with the top four candidates all bunched between 17 percent and 20 percent.

About six-in-10 likely caucus-goers, 59 percent, say their minds are made up — including 65 percent of Sanders supporters, 65 percent of Biden backers and 64 percent of Buttigieg voters.

Because of the nature of the caucus process — two rounds of voting at each caucus site, including the elimination of low-polling candidates deemed “not viable” — polls in Iowa reflect voters’ initial preferences, but not necessarily the final outcome. Still, the New York Times/Siena poll attempts to gauge voters’ second choices, which may determine how they behave on Feb. 3 if their initial preference is eliminated after the first alignment.

Among Sanders’ supporters, a plurality, 44 percent, would pick Warren, a fellow liberal candidate. The majority of Warren’s voters, meanwhile, are split between Sanders (37 percent) and Klobuchar (23 percent).

Caucus-goers are only allowed to choose another candidate if their first choice does not meet the viability threshold at their precinct, which is 15 percent in the vast majority of caucus sites.

The candidates polling well below Klobuchar include businessman Tom Steyer (3 percent), entrepreneur Andrew Yang (3 percent), Rep. Tulsi Gabbard of Hawaii (1 percent), former New York City Mayor Mike Bloomberg (1 percent), Sen. Michael Bennet of Colorado (0 percent), former Rep. John Delaney of Maryland (0 percent) and former Massachusetts Gov. Deval Patrick (0 percent). Eight percent of caucus-goers are undecided.

For Democrats who worry that nominating Sanders — a self-avowed “democratic socialist” who is proposing a massive expansion of the federal government — will hurt the party’s chances of defeating President Donald Trump in the fall, the New York Times/Siena poll will offer little to ease their concerns.

In a general-election matchup in Iowa — a swing state Barack Obama carried twice before Trump flipped it in 2016 — Trump leads Sanders by 6 points, the poll shows, 48 percent to 42 percent. That’s a slightly larger margin than Trump has over other Democrats: He leads Buttigieg by 1 point, Biden by 2 points and both Warren and Klobuchar by 5 points.

The poll also tested Bloomberg — who is not competing in next month’s caucuses and is instead focused on states that vote later in the nominating process — against Trump, and he fares the worst. Trump leads Bloomberg, 47 percent to 39 percent.

Trump’s approval rating in the state is 51 percent, according to the poll, a little higher than his 46 percent disapproval rating.

Only 41 percent of Iowa voters would approve of the Senate removing Trump from office at the conclusion of the ongoing impeachment trial, while 53 percent would disapprove of Trump’s removal. (The poll was conducted partly before House Democrats began their three days of arguments on the Senate floor this week.)

The New York Times/Siena College poll was conducted Jan. 20-23, surveying 1,689 registered Iowa voters. The margin of error is plus or minus 2.8 percentage points.

For the sample of 584 likely Democratic caucus-goers, the margin of error is plus or minus 4.8 percentage points.