Sen. Elizabeth Warren Elizabeth WarrenHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline Democratic senators ask inspector general to investigate IRS use of location tracking service MORE is now the most serious rival to former Vice President Joe Biden Joe BidenPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Hillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Fox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio MORE for the Democratic nomination in 2020.

Several recent polls, both nationwide and in Iowa, have shown the Massachusetts senator in second place to Biden. Her performances at televised debates have won widespread praise. And her fundraising has been robust. She raised $19 million in the second quarter.

But if Warren is the one major candidate who is unquestionably on an upward trajectory, there are still significant questions about how she gets past Biden, who continues to lead by a sizable margin in most polls.

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The former vice president is particularly popular with black voters, who are pivotal to success in a Democratic primary.

Among progressives, there are also worries about a split in the left-wing vote between Warren and Sen. Bernie Sanders Bernie SandersThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Bernie Sanders: 'This is an election between Donald Trump and democracy' The Hill's 12:30 Report: Trump stokes fears over November election outcome MORE (I-Vt). Even if Warren emerges as the clear standard-bearer of the left in the months ahead, Sanders is not going anywhere.

“The progressive voters have to coalesce at some point behind either Bernie Sanders or Elizabeth Warren, because that way we can win,” said left-wing writer and activist Jonathan Tasini. “They can be the nominee if the forces marshal behind one of them. If they don’t, we certainly risk the splitting of that vote.”

Several polls in recent days have suggested that Warren is moving past Sanders, who has so far been unable to recapture the magic that made him a tough challenger to eventual nominee Hillary Clinton Hillary Diane Rodham ClintonFox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio Trump, Biden court Black business owners in final election sprint The power of incumbency: How Trump is using the Oval Office to win reelection MORE in 2016.

A Monmouth University poll in Iowa released Thursday showed Warren with 19 percent support to Sanders’s 9 percent. Biden was leading the field with 28 percent. Sen. Kamala Harris Kamala HarrisHundreds of lawyers from nation's oldest African American sorority join effort to fight voter suppression Biden picks up endorsement from progressive climate group 350 Action 3 reasons why Biden is misreading the politics of court packing MORE (D-Calif.) was third with 11 percent support.

One national poll from The Economist and YouGov saw Warren trailing Biden by 6 points (16 percent to 22 percent) with Sanders in third on 13 percent.

A second national poll, from Quinnipiac University, had Warren 7 points clear of Sanders — 21 percent to his 14 percent — though she still trailed Biden by 11 points.

Democratic strategist Tad Devine, who worked for Sanders in 2016 but is not aligned with any candidate this cycle, acknowledged that Warren’s performances in the debates have helped her.

But he also asserted that the clarity and power of her pitch on the campaign trail were at the heart of her appeal.

“She has a very strong message,” Devine said, drawing a parallel with how a similar message from Sanders resonated in 2016. “The idea that someone is willing to fight for people, and against an economy that is rigged against them? That carries a lot of weight with Democratic primary voters — and with general election voters.”

Warren’s grasp of detail — an early slogan, including on her official merchandise, was “Warren has a plan for that” — has also been an asset, as has her willingness to insist that Democrats must dream big.

She delivered one of the most memorable moments of the debates in Detroit late last month when, in response to a centrist critique from former Rep. John Delaney John DelaneyCoronavirus Report: The Hill's Steve Clemons interviews Rep. Rodney Davis Eurasia Group founder Ian Bremmer says Trump right on China but wrong on WHO; CDC issues new guidance for large gatherings The Hill's Coronavirus Report: Kansas City Mayor Quinton Lucas says country needs to rethink what 'policing' means; US cases surpass 2 million with no end to pandemic in sight MORE (D-Md.), she shot back: “I don't understand why anybody goes to all the trouble of running for president of the United States just to talk about what we really can't do and shouldn't fight for.”

But if Warren has strong momentum, she also faces some high hurdles.

In The Economist’s national poll, Biden enjoyed more than double her support among black voters (33 percent to 13 percent) even while Warren was a single point ahead of him among white voters (20 percent to 19 percent).

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In the Quinnipiac national poll, she was just 3 points adrift of him among white voters (30 percent to 27 percent) but was getting crushed with black voters (47 percent to 8 percent).

There has been some anecdotal evidence that Warren can forge a connection with black voters, especially women, when she gets to address diverse crowds in person. But that has yet to translate into concrete results in the polls.

The battle for African American support is further complicated by the fact that Sanders is showing more traction among nonwhites than he did four years ago, and two black senators — Harris and Sen. Cory Booker Cory Anthony Booker3 reasons why Biden is misreading the politics of court packing Bipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility MORE (D-N.J.) — are in the race this year.

There is also the question of whether the social media chatter about the contest fosters the impression that the party as a whole is more left-wing — and therefore more likely to select someone like Warren as its nominee — than is actually the case.

Moderate Democrats vote in the primaries, too — and poll after poll have shown they are much more drawn to Biden than to Warren or Sanders.

In the YouGov poll, Warren led Biden among Democrats who identified as liberal (22 percent to 18 percent) but trailed him badly among moderates (10 percent to his 33 percent).

A Democratic strategist who asked for anonymity but is not aligned with any 2020 candidate, pointed out another potential problem. Warren will at some point have to demonstrate that she can cut into Biden’s support.

“The good news for Warren is that she is rising in the polls and former Sanders voters are moving toward her,” the strategist said. “The bad news is, it’s not coming from Biden voters. As long as that stays the case — and Sanders stays in the race — then it’s hard to see how she gets over that hump.”

But several sources who spoke to The Hill cautioned against drawing too many conclusions this early in the race.

Notably, there was a common consensus that if Warren were to win the Iowa caucuses — something that is plausible given the liberal lean of caucusgoers — that could reorder the race at a stroke.

“I could see her getting into a very competitive position,” Devine said, recalling how, when then-Sen. Barack Obama Barack Hussein ObamaObama warns of a 'decade of unfair, partisan gerrymandering' in call to look at down-ballot races Quinnipiac polls show Trump leading Biden in Texas, deadlocked race in Ohio Poll: Trump opens up 6-point lead over Biden in Iowa MORE (D-Ill.) won the caucuses in 2008 while Hillary Clinton trailed in third, “everything changed overnight.”

For now, Warren is in the hunt. And it’s game on.