Although Joe Biden is still ahead of his other rivals in the polls, the unity of Elizabeth Warren and Bernie Sanders and the resignation of one of them can affect the scene of the US presidential election. New polls have led to the fear and anxiety of Joe Biden and his companions. Here's an overview of these surveys and analyzes:

Biden edges higher atop field of 2020 Democrats: poll

As The Hill reported, Former Vice President Joe Biden increased his lead atop a crowded field of Democratic presidential candidates by 2 points, a new poll finds.Biden now has the support of 33 percent of Democratic primary voters across the nation, according to the Morning Consult survey, 13 points above the next-most popular candidate, Sen. Bernie Sanders .Rounding out the top five are Sen. Elizabeth Warren (D-Mass.) at 15 percent, followed by Sen. Kamala Harris (D-Calif.) at 8 percent and South Bend, Ind., Mayor Pete Buttigieg at 5 percent, the poll shows.Among early voters in Iowa, New Hampshire, South Carolina or Nevada, Biden maintains a 16-point lead over Sanders, who is followed by Warren, Harris and billionaire Tom Steyer, according to Morning Consult.The results come as Biden’s electability argument is showing signs of weakness, with a survey from Monmouth University on Monday showing the former vice president’s support slipping to below 20 percent. The results mark a double-digit decline from its last poll in June and put him in a three-way tie nationally with Sanders and Warren.

Democrats have cited the poll as evidence Biden isn’t suitable to earn the party’s presidential nomination and isn’t the candidate best equipped to defeat President Trump in 2020 — a central focus of the party in choosing a nominee.The Morning Consult poll surveyed more than 17,300 voters between Aug. 19 and Aug. 25. Its margin of error is 1 percent.

Poll: Bernie, Warren surge to tie Biden atop Democratic field

On the  other hand, Politico reported that 'The main takeaway,' says Monmouth University's pollster, 'is that the Democratic race has become volatile.Bernie Sanders and Elizabeth Warren have surged to tie with Joe Biden atop the Democratic presidential field, according to a poll that suggests the three are solidifying their status as the top tier in the massive field.The Monmouth University poll, released Monday, shows Sanders and Warren deadlocked among Democratic voters at 20 percent, with Biden a point behind, at 19 percent. No other candidate cracks double digits: Kamala Harris is in fourth place, at 8 percent.

Compared with the Monmouth poll in June, Sanders has ticked up 6 points, and Warren 5 points. Biden dropped 13 points, from 32 percent in June.The poll shows Biden’s slippage coming across the Democratic electorate, rather than from a specific demographic or ideological group. He is down 14 points among white and nonwhite voters. He’s down 14 points among men, and 13 points among women. He’s down 15 points among voters younger than 50 years old, and 9 percent among voters 50 and older.

Biden also slipped 18 points among Democratic voters who described themselves as moderate or conservative, and 9 points among self-identified liberals.“The main takeaway from this poll is that the Democratic race has become volatile,” said Patrick Murray, director of the Monmouth University Polling Institute. “Liberal voters are starting to cast about for a candidate they can identify with. Moderate voters, who have been paying less attention, seem to be expressing doubts about Biden. But they are swinging more toward one of the left-leaning contenders with high name recognition rather than toward a lesser known candidate who might be more in line with them politically.”

The Monmouth poll is the first major national poll all year to show a candidate other than Biden in the lead. It differs from some surveys conducted over similar time periods. A CNN/SSRS national poll, conducted Aug. 15-18, showed Biden at 29 percent, significantly ahead of Sanders (15 percent) and Warren (14 percent.)

The Monmouth poll, which was conducted Aug. 16-20, surveyed 298 Democratic voters. The margin of error is plus or minus 5.7 percentage points.Once the most popular candidate in the race, the Monmouth poll shows Biden’s favorable rating slipping, from 74 percent in June to 66 percent now. That is similar to favorable ratings for Warren (65 percent) and Sanders (64 percent)But the percentage of Democratic voters who view Biden unfavorably has increased from 17 percent in June to 25 percent now. Warren’s unfavorable rating, 13 percent, is significantly lower, while Sanders matches Biden with a 24 percent unfavorable score.Aside from the top three candidates — plus Harris in fourth place — no other candidate earns 5 percent support. Cory Booker and Pete Buttigieg are at 4 percent, and entrepreneur Andrew Yang is at 3 percent. Tying for eighth place at 2 percent are Juli?n Castro, Beto O’Rourke and Marianne Williamson.

Monmouth University's poll is approved by the Democratic National Committee for deciding which candidate's make the primary debates. But this survey offers virtually no help to candidates who haven’t already qualified for the third debate next month in Houston ahead of Wednesday’s deadline.Candidates need to earn at least 2 percent in four DNC-approved polls released between June 28 and Wednesday, and receive donations from 130,000 individuals over the duration of the campaign. Ten candidates have already qualified: Biden, Warren, Sanders, Harris, Buttigieg, Booker, Sen. Amy Klobuchar, Castro, Yang and O’Rourke.

Tom Steyer’s campaign says it has received donations from more than 130,000 people, but he is one poll short, having only earned 2 percent in three DNC-approved surveys. Monday’s Monmouth poll showed him at 0 percent.Tulsi Gabbard has also met the donor threshold, but she is still two polls shy of the polling threshold after earning 1 percent in the Monmouth survey. Williamson has also crossed the donor mark, but her 2 percent in the Monmouth poll was only her first qualifying poll — and it’s highly unlikely she’ll get three more polls over the next two-and-a-half days.

3-Way Lead as Dem 2020 Picture Shifts

West Long Branch, NJ – Vermont Sen. Bernie Sanders, Massachusetts Sen. Elizabeth Warren, and former Vice President Joe Biden are currently bunched together in the national Democratic presidential preference contest. Movement in the latest Monmouth University Poll – positive for Warren and Sanders, negative for Biden – suggests the 2020 presidential nomination process may be entering a volatile stage.  The poll results also suggest that liberal voters are starting to take a closer look at a wider range of candidates, while moderates are focusing on those with the highest name recognition.  Another key finding that could contribute to growing volatility in the race is confusion over “Medicare for All.” Most say support for this policy is an important factor in choosing a Democratic nominee, but voters actually prefer a public option over a single payer plan.

The poll finds a virtual three-way tie among Sanders (20%), Warren (20%), and Biden (19%) in the presidential nomination preferences of registered Democrats and Democratic-leaning voters across the country. Compared to Monmouth’s June poll, these results represent an increase in support for both Sanders (up from 14%) and Warren (up from 15%), and a significant drop for Biden (down from 32%.)

Results for the rest of the field are fairly stable compared to two months ago. These candidates include California Sen. Kamala Harris at 8% support (identical to 8% in June), New Jersey Sen. Cory Booker at 4% (2% in June), South Bend Mayor Pete Buttigieg at 4% (5% in June), entrepreneur Andrew Yang at 3% (2% in June), former cabinet secretary Juli?n Castro at 2% (<1% in June), former Texas Rep. Beto O’Rourke at 2% (3% in June), and author Marianne Williamson at 2% (1% in June). Support for the remaining 13 candidates included in the preference poll registered only 1% or less.Biden has suffered an across the board decline in his support since June.  He lost ground with white Democrats (from 32% to 18%) and voters of color (from 33% to 19%), among voters without a college degree (from 35% to 18%) and college graduates (from 28% to 20%), with both men (from 38% to 24%) and women (from 29% to 16%), and among voters under 50 years old (from 21% to 6%) as well as voters aged 50 and over (from 42% to 33%).  Most of Biden’s lost support in these groups shifted almost equally toward Sanders and Warren.

“The main takeaway from this poll is that the Democratic race has become volatile.  Liberal voters are starting to cast about for a candidate they can identify with.  Moderate voters, who have been paying less attention, seem to be expressing doubts about Biden. But they are swinging more toward one of the left-leaning contenders with high name recognition rather than toward a lesser known candidate who might be more in line with them politically,” said Patrick Murray, director of the independent Monmouth University Polling Institute.  He added, “It’s important to keep in mind this is just one snapshot from one poll.  But it does raise warning signs of increased churning in the Democratic nomination contest now that voters are starting to pay closer attention.”

Biden lost support over the past two months among Democrats who call themselves moderate or conservative (from 40% to 22%) with the shift among these voters accruing to both Sanders (from 10% to 20%) and Warren (from 6% to 16%).  Biden also lost support among liberals (from 24% to 15%), but this group’s backing has scattered to a variety of other candidates. Sanders has picked up a few points among liberal voters (from 17% to 21%) while Warren has held fairly steady (from 25% to 24%).  Also, Harris has not budged with this group (from 10% to 11%) and Buttigieg has slipped slightly (from 8% to 5%).  However, the aggregate support for four other candidates – namely Booker, Castro, Williamson and Yang – has gone up a total of 8 points among liberal Democrats (from 8% to 16% for the four combined.)

The Monmouth poll also finds that Biden has lost his small edge in the early states where Democrats will cast ballots from February through Super Tuesday. His even larger lead in the later states has vanished as well.  Biden (20%), Warren (20%), Sanders (16%), and Harris (12%) are all in the top tier among voters in the early states. Biden has slipped by 6 points since June and Warren has gained 5 points over the same time span.  Early state support for Sanders and Harris has not changed much.  In the later states, Biden’s support has plummeted from 38% in June to 17% now, while both Warren (from 16% to 20%) and Sanders (from 13% to 23%) have made gains.

“Biden’s drop in support is coming disproportionately from later states that have less impact on the process. But if this trend continues it could spell trouble for him in the early states if it undermines his claim to being the most electable candidate.  This could benefit someone like Harris, who remains competitive in the early states and could use a strong showing there to propel her into the top tier.  Based on the current data, though, Warren looks like the candidate with the greatest momentum right now,” said Murray.