Former Vice President Joe BidenJoe BidenTrump says he doesn't want NYT in the White House Warren to protest with striking Chicago teachers Schiff punches back after GOP censure resolution fails MORE has extended his lead over progressive rivals Sens. Elizabeth WarrenElizabeth Ann WarrenWarren to protest with striking Chicago teachers Overnight Health Care — Presented by Partnership for America's Health Care Future — Four companies reach 0M settlement in opioid lawsuit | Deal opens door to larger settlements | House panel to consider vaping tax | Drug pricing markup tomorrow On The Money: Trump dismisses 'phony Emoluments Clause' after Doral criticism | Senate Dems signal support for domestic spending package | House panel to consider vaping tax MORE (D-Mass.) and Bernie SandersBernie SandersWarren to protest with striking Chicago teachers Sanders: 'Outrageous' to suggest Gabbard 'is a foreign asset' Democratic strategist: Sanders seeking distance from Warren could 'backfire' MORE (I-Vt.) in the latest Hill-HarrisX poll released on Monday. 

The poll of likely Democratic and independent voters found that 31 percent support Biden for president, a 4-point increase from the last time the poll was conducted in late August.

Sanders came in second with 16 percent, while Warren followed in third place with 14 percent.

Though still within the margin of error, this uptick in support for Biden is a positive for a campaign that is trying to hold off Warren.

A Des Moines Register/CNN/Mediacon poll released Saturday showed Warren overtaking Biden for the first time in the caucus state. Warren won 22 percent support in the poll, compared to 20 percent for Biden. 

In the Hill/HarrisX poll, South Bend, Ind., Mayor Pete ButtigiegPeter (Pete) Paul ButtigiegSanders: 'Outrageous' to suggest Gabbard 'is a foreign asset' Hillicon Valley: Facebook removes Russian, Iranian accounts trying to interfere in 2020 | Zuckerberg on public relations blitz | Uncertainty over Huawei ban one month out Clinton attacks on Gabbard become flashpoint in presidential race MORE tied Sen. Kamala HarrisKamala Devi HarrisClinton attacks on Gabbard become flashpoint in presidential race Poll: Biden holds 10-point lead nationally over Warren Trump declines to participate in Weather Channel 2020 climate change special MORE (D-Calif.) for fourth place, with each winning 5 percent.

Former Texas congressman Beto O’Rourke (D) followed with 4 percent.

Former entrepreneur Andrew YangAndrew YangOn The Money: Trump dismisses 'phony Emoluments Clause' after Doral criticism | Senate Dems signal support for domestic spending package | House panel to consider vaping tax Sanders: 'Outrageous' to suggest Gabbard 'is a foreign asset' Clinton attacks on Gabbard become flashpoint in presidential race MORE dropped back to 2 percent after previously climbing to 5 percent.

The only other candidates to poll at least 2 percent or higher were Sen. Cory BookerCory Anthony BookerPoll: Biden holds 10-point lead nationally over Warren Trump declines to participate in Weather Channel 2020 climate change special Bennet: Warren 'not being honest about' her 'Medicare for All' plan MORE (D-N.J.), Amy KlobucharAmy Jean KlobucharPoll: Biden holds 10-point lead nationally over Warren Robert Reich sees Democratic race as Warren, Sanders and Biden: 'Everyone else is irrelevant' Democrats lead Trump by wide margins in Minnesota MORE (D-Minn.), and former Housing and Urban Development Secretary Julián Castro.

HarrisX researchers surveyed 440 Democratic and independent voters between Sept. 20 and Sept. 21. The margin of error for this poll is plus or minus 4.7 percentage points.

The Democratic field narrowed last week after New York City Mayor Bill de Blasio dropped out of the 2020 presidential race averaging in several national polls at less than 1 percent.

De Blasio, who first launched his bid in May, announced the news on MSNBC’s “Morning Joe,” and vowed to continue his work as mayor of New York City.

“It’s clearly not my time, so I’m going to end my presidential campaign, continue my work as mayor of New York City, and I'm going to keep speaking up for working people," he said at the time.

—Tess Bonn