Washington (CNN) Three new national polls find that former Vice President Joe Biden and Sens. Elizabeth Warren and Bernie Sanders are leading the pack of Democratic presidential candidates less than 100 days before the Iowa caucuses, the first real test of the 2020 Democratic primary.

Biden is at 28% among Democratic voters and independents who lean Democratic, while Warren, a Massachusetts Democrat, is at 23% and Sanders, a Vermont independent, is at 17%, according to a Washington Post-ABC News poll released Sunday. In the September iteration of the poll , the former vice president had nearly the same amount of support while Warren was at 18% and Sanders was at 19%. South Bend, Indiana, Mayor Pete Buttigieg is at 9% in the new poll, up from the 4% he had last month. No other candidate received above 2% in the poll.

Meanwhile, an NBC News-Wall Street Journal poll -- also released Sunday -- suggests a tighter contest with Warren's 23% within striking distance of Biden's 27%, and Sanders at 19% among Democratic voters. The poll also showed Buttigieg at 6%, Minnesota Sen. Amy Klobuchar at 5% and Harris at 4%. Four-percent of voters in the poll picked Yang as their preferred candidate, while none of his opponents received above 2%.

The polls come two days after the field lost a candidate -- former Texas Rep. Beto O'Rourke, who struggled to gain a decent amount of support in recent national polls.

Who can beat Trump?

Democratic voters think Biden has the best chance to beat President Donald Trump , according to the Washington Post-ABC News poll, but they didn't place the former vice president before his competitors when it came to five other categories, including mental sharpness and policy issues. Warren, on the other hand, led the pack when it came to mental sharpness, with 24% of Democrats saying she has the sharpest mental ability.

Additionally, among the three oldest Democratic candidates -- Biden, Sanders and Warren -- voters were about evenly divided in that poll on whether Sanders was physically fit enough for the presidency. The concerns over Sanders' health comes after he suffered a heart attack in early October that forced him to take a break from the campaign trail. In the wake of the heart attack, Sanders said he won't be able to keep up the robust schedule he and his supporters have become accustomed to during campaigns.

Eighty percent of Democrats and Democratic-leaning independents believe Warren is healthy enough to serve as president, and 74% agree that Biden is healthy enough for the Oval Office.

The Washington Post-ABC News poll was conducted by phone from October 27-30 in English and Spanish among a random national sample of 1,003 US adults reached by landlines and cellphones. The results have a margin of sampling error of of plus or minus 5.5 percentage points among the sample of 452 Democrats and Democratic-leaning independent adults and is plus or minus six points among the sample of 402 Democratic-leaning registered voters.

The Fox News poll was conducted by phone from October 27-30 from a random sample of 1,040 registered voters. The results have a margin of sampling error of plus or minus 4.5 percentage points among the sample of 471 Democratic primary voters.

The NBC News-Wall Street Journal poll was conducted by phone from October 27-30 from a random sample of 900 adults. The results have a margin of sampling error of plus or minus 4.8 percentage points among the sample of 414 Democratic primary voters.