Former Vice President Joe Biden has been the frontrunner of the Democratic primary race to this point, but he's at risk of losing his spot at the top to Sen. Elizabeth Warren, the progressive firebrand senator.

Warren is the only candidate in the Democratic field whose support and favorability has surged over time while Biden's has decreased, even among groups that disproportionately support him.

Biden's support in Morning Consult's weekly Democratic primary survey has fallen by three percentage points since mid-March while Warren's has doubled in the same timeframe.

In Monmouth University polling alone, Warren's net favorability has increased by six percentage points since May while Biden's has decreased by a full 19 percentage points.

And while many pundits have questioned Warren's "likability" since her first run for office in 2012, she currently has the highest net favorability rating out of the entire Democratic field at +54.

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Former Vice President Joe Biden has been the frontrunner of the Democratic primary race so far, but he's at risk of losing his spot at the top to Sen. Elizabeth Warren, the progressive firebrand senator.

Warren, who entered the race last December, has experienced a meteoric rise in basically every possible metric. She's up in Democratic primary polls, approval rating, fundraising, and even crowd size, while Biden's support and favorability are dwindling down over time.

Initially, her campaign struggled to gain traction amid controversy over a DNA test Warren took to confirm her Native American heritage and her surprising decision to completely swear off all private fundraisers, prompting her finance director to quit.

But in the following months, Warren proved her detractors wrong by fully embracing the role of the policy wonk. She's released a unique and detailed policy plan to address almost every imaginable issue from the cost of college to the opioid crisis, rolling out so many policies that "I've got a plan for that" has become her unofficial slogan.

Read more: The 2020 Democratic field is slowly narrowing. Elizabeth Warren supporters tell us why they think she can go the distance.

While her choice to eschew private fundraisers was initially seen as a huge liability, not courting wealthy donors has enabled Warren to spend more time on the campaign trail, where she has thrived.

And on the eve of the next narrowed-down Democratic primary debate, Warren appears to be overtaking Sen. Bernie Sanders as the 2020 field's progressive standard-bearer, while Biden's stronghold on the race is fading fast.

Warren is the only candidate who has experienced a consistent rise in Democratic primary polls

Despite a recent Monmouth University poll that showed Biden, Sanders, and Warren in a three-way tie with 19% to 20% of the vote each, Biden is still the frontrunner in Real Clear Politics' polling tracker with an average of 28% support, followed by Sanders at 17.7%, and Warren in a close third at 16%.

Monmouth acknowledged their poll showing the three candidates neck-and-neck was an "outlier," But Warren is the only major candidate who has consistently and steadily gained support over time, a huge warning sign for Biden.

In a Suffolk University/USA Today poll and a Quinnipiac University poll all released the next day on August 28, Biden lead with 32% of the vote in both surveys followed by Warren in second place and Sanders in third.

In May, shortly after the former Veep entered the race, Morning Consult's weekly Democratic primary tracking poll showed Biden polling at 40%, compared to Warren at 8%. Since then, Biden's support has dropped by three percentage points to 33% while Warren's has increased to 15% as of this week.

Warren's surging support is not just outpacing Biden, but she and Andrew Yang been the only candidates to see their levels of support double in Morning Consult since mid-March, when Warren polled at 7%.

Read more: Don't buy into the hype that Joe Biden is necessarily the most electable Democrat

And while many pundits have questioned Warren's "likability" since her first run for office in 2012, she currently has the highest net favorability rating out of the entire Democratic field at +54 — compared to +52 for Biden and +51 for Sanders, according to a FiveThirtyEight analysis.

In Monmouth polling alone, Warren's net favorability has increased by six percentage points since May while Biden's has decreased by a full 19 percentage points.

Adam Green, a Democratic strategist and the co-founder of the Progressive Change Campaign Committee, which has endorsed Warren, told Insider in a Tuesday interview that he's traveled to many Warren rallies around the country everywhere from Iowa to Mississippi.

"Part of what we see as the reason for her rise in the polls is that voters fall in love with her when they hear how she merges her big plans with her very personal story of struggle growing up poor in Oklahoma and being a single mom in Texas," Green said.

"She both speaks to people's heads and their hearts, and for the many electability voters out there who want to beat Trump, they see Warren as the only candidate who gets standing ovations in many forums. The phenomenon of success begets success," he added.

Elizabeth Warren and former Vice President Joe Biden. REUTERS/Jonathan Ernst

Warren is on her way to eclipsing Biden as the most electable candidate and replacing Sanders as the progressive standard-bearer

Biden has been the frontrunner in Democratic primary polls largely due to the high levels of support he enjoys among two crucial demographics that consistently turn out in Democratic primaries: African-American voters and seniors.

The former vice president benefits not only from his name recognition but because he is perceived in most polls as the Democratic candidate most likely to defeat Trump in a general election — which older voters in particular heavily prioritize over electing a nominee that best aligns with their policy positions.

The Monmouth poll also found that not only has Biden "lost his edge" in both early and late primary states, he is rapidly losing ground within the subgroups that disproportionately support him, including voters of color, older voters, and those without a college degree.

"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," Monmouth University polling director Patrick Murray said in a Monday release, noting that Biden is losing the support of moderate and conservative Democratic voters to more progressive candidates like Warren and Sanders.

Read more: Conservatives say Democrats should adopt centrist policies if they want to win back Trump voters. But there's a much more effective way for them to defeat Trump

As Bloomberg recently reported, the percentage of Democrats who think Biden could beat Trump in Economist/YouGov polling has remained steady all summer at 65%.

But as Sen. Elizabeth Warren has surged in Democratic primary polls, the percentage of respondents who believe Warren could defeat Trump has increased by 14 percentage points from 43% to 57% in the exact same timeframe — even as both candidates net favorability ratings remained virtually the same in YouGov/Economist polling.

In Insider's recurring SurveyMonkey audience polling as well, the percentage of Democratic primary voters who believe Warren could beat Trump has soared from 30% in mid-February to 48% in August. (Read more about how our polling works here).

Green told Insider that unlike Biden, Warren is showing voters she's the most electable candidate by inspiring them with her own unique agenda and vision, instead of explicitly trying to convince everyone of her own electability.

"There's some candidates who say, literally, I am the most electable. What Elizabeth Warren does is she goes to places like Mississippi and Texas and Iowa, get standing ovations, and has everyone from African-American voters and young people to former Trump voters leaving the room supporting her," he said.

And over the weekend, Warren drew huge crowds of 12,000 to 15,000 supporters at campaign rallies in Minnesota and Washington, while Biden had to contend with a stream of unfortunate gaffes on the campaign trail, and headlines arguing his campaign is experiencing an "enthusiasm gap" and an "Iowa problem."

Of course, crowd sizes certainly aren't a scientifically perfect metric by which to gauge enthusiasm, and aren't necessarily predictive of general election results.

But Warren's rising levels of support, favorability, and perceived electability taken together with the decline in Biden's support across the board show that the former vice president's days of comfortably leading the Democratic field could be numbered.