Biden, Sanders, Warren support dips in new poll

Top-tier candidates, including former Vice President Joe BidenJoe BidenSupport for impeachment inches up in poll Overnight Defense: Trump's Syria envoy wasn't consulted on withdrawal | McConnell offers resolution urging Trump to rethink Syria | Diplomat says Ukraine aid was tied to political investigations Democrats say they have game changer on impeachment MORE and Sen. Bernie SandersBernie SandersOvernight Health Care — Presented by Partnership for America's Health Care Future — ObamaCare premiums dropping for 2020 | Warren, Buttigieg shift stances on 'Medicare for All' | Drug companies spend big on lobbying Mellman: Trumping peace and prosperity Tlaib to join Sanders at campaign rally in Detroit MORE, saw a dip in support over the past two weeks while several lower-tier candidates saw a slight uptick in their numbers, according to the latest Hill-HarrisX poll released on Wednesday.

The survey showed that 31 percent of likely Democratic primary voters back Biden, marking a 3 point drop from an identical poll conducted two weeks ago.

It also found a drop in support for Sanders and Sen. Elizabeth WarrenElizabeth Ann WarrenOvernight Health Care — Presented by Partnership for America's Health Care Future — ObamaCare premiums dropping for 2020 | Warren, Buttigieg shift stances on 'Medicare for All' | Drug companies spend big on lobbying Mellman: Trumping peace and prosperity On The Money: Waters clashes with Trump officials over 'disastrous' housing finance plan | Dems jump into Trump turf war over student loans | House passes bill targeting anonymous shell companies MORE (D-Mass.), the only other two candidates in double figures in the poll.

Sanders’s support dipped 4 points to 16 percent, while Warren’s support dropped 2 points to 10 percent.

Sen. Kamala HarrisKamala Devi HarrisSaagar Enjeti: Warren, Buttigieg don't stand a chance against Trump Warren overtakes Sanders in new poll The Hill's 12:30 Report: Trump faces backlash for comparing impeachment to 'lynching' MORE (D-Calif.) retained her spot in fourth place but her 7 percent support is a decrease of 2 points since the July 29 poll. South Bend, Ind., Mayor Pete ButtigiegPeter (Pete) Paul ButtigiegOvernight Health Care — Presented by Partnership for America's Health Care Future — ObamaCare premiums dropping for 2020 | Warren, Buttigieg shift stances on 'Medicare for All' | Drug companies spend big on lobbying Poll: Biden holds 2 point lead over Sanders nationally Saagar Enjeti: Warren, Buttigieg don't stand a chance against Trump MORE rounded out the top five with 4 percent, a 1 point dip over the past two weeks.

Former Texas congressman Beto O’Rourke, meanwhile, held onto to sixth place with 4 percent support, which is unchanged from two weeks ago.

The number of undecided voters ticked back up to 10 percent, after briefly dropping to 8 percent.

A handful of lower-tier candidates received a slight boost. 

Gov. Steve BullockSteve BullockSuper PAC seeks to spend more than million supporting Yang The Hill's Campaign Report: Biden camp faces new challenges Private flight spending soars in Democratic presidential race MORE (D-Mont.), former San Antonio Mayor Julián Castro (D), and Sen. Amy KlobucharAmy Jean KlobucharHillicon Valley: Zuckerberg would support delaying Libra | More attorneys general join Facebook probe | Defense chief recuses from 'war cloud' contract | Senate GOP blocks two election security bills | FTC brings case against 'stalking' app developer Senate Republicans block two election security bills Warren overtakes Sanders in new poll MORE (D-Minn.) all ticked up one point to two percent. Best-selling author Marianne WilliamsonMarianne WilliamsonMarianne Williamson on impeachment: Trump's actions 'too perilous' not to continue inquiry Marianne Williamson: DNC is 'dictating' rather than 'facilitating the process of democracy' Marianne Williamson explains how she, Tulsi, and Yang have been marginalized MORE, who had a breakout moment during the second round of Democratic debates, saw a two-point jump to 2 percent. 

The latest poll comes as a number of 2020 White House contenders make the rounds in Iowa to make their case to caucus goers.

Though the Iowa caucuses are still six months away, virtually every candidate has made an appearance at the Iowa State Fair, which is considered an essential campaign stop for presidential hopefuls on both sides of the aisle.

Many of the candidates are also scrambling to qualify for the next round of Democratic primary debates in September.

The Hill-HarrisX poll was conducted among 451 Democratic and Democratic-leaning independent voters with a margin of error of plus or minus 4.6 percentage points.

—Tess Bonn