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 (D-Mass.) is closing in on 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 in Iowa, according to a Monmouth University poll released Thursday.

Biden remains the contest's front-runner, notching 28 percent support among likely Democratic caucusgoers in Iowa. But Warren is now polling in second place with 19 percent support, a significant gain from the 7 percent she carried in a similar survey conducted in April.

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In third place is 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.), who came in with 11 percent support in the Hawkeye State. Like Warren, she saw a bump since Monmouth’s last Iowa poll, gaining 4 points since April.

Meanwhile, 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.) has trended in the opposite direction. He took fourth in the latest survey with 9 percent support, down from 16 percent in April. He’s trailed closely by South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice MORE (D) at 8 percent, according to the poll.

Four other candidates notched above 1 percent in the Monmouth poll of Iowa Democratic caucusgoers: Sen. Amy Klobuchar Amy Klobuchar3 reasons why Biden is misreading the politics of court packing Social media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight MORE (D-Minn.) and billionaire philanthropist Tom Steyer Tom SteyerTV ads favored Biden 2-1 in past month Inslee calls Biden climate plan 'perfect for the moment' OVERNIGHT ENERGY: Trump administration finalizes plan to open up Alaska wildlife refuge to drilling | California finalizes fuel efficiency deal with five automakers, undercutting Trump | Democrats use vulnerable GOP senators to get rare win on environment MORE scored 3 percent each, while Sen. Kirsten Gillibrand Kirsten GillibrandSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Suburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits MORE (D-N.Y.) and former tech executive Andrew Yang Andrew YangDoctor who allegedly assaulted Evelyn Yang arrested on federal charges The Hill's Campaign Report: Biden weighs in on police shootings | Who's moderating the debates | Trump trails in post-convention polls Buttigieg launches his own podcast MORE came in with 2 percent each.

Warren’s rise suggests that her massive field operation in Iowa and breakneck pace of campaigning may be paying off. She has more staffers on the ground than any of her rivals, and is among the top-tier candidates who have spent the most time in the state, according to the Des Moines Register, which is tracking candidate visits to Iowa.

The poll, which was conducted from Aug. 1 to 4, also suggests that Warren’s standing may have been buoyed by what was considered by many to be a solid performance in the second Democratic primary debate last week.

More than three quarters of Iowa Democratic caucusgoers — 76 percent — have a positive impression of Warren, the Monmouth poll found, giving her the highest favorability rating of any candidate in the race. Biden takes a close second on that front, with 73 percent reporting favorable views of the former vice president.

Harris and Buttigieg are tied at 68 percent favorability, while Sanders rounds out the top five at 58 percent.

The Iowa caucuses are still roughly six months away, however, and the candidates will have an opportunity in the coming days to boost their Iowa bona fides. Virtually the entire Democratic field is slated to speak at the Iowa State Fair, one of the most essential stops for presidential campaigns.

The Monmouth poll surveyed 401 likely Democratic caucusgoers in Iowa, about 20 percent whom said they would likely caucus online or on the phone, from Aug. 1 to 4. It has a margin of error of plus or minus 4.9 percentage points.