Former Vice President Joe Biden’s lead in the Democratic primary has been cut in half, according to a new poll out Wednesday, and while Biden still maintains his grip on frontrunner status, the CNN poll shows Sens. Elizabeth Warren and Bernie Sanders incrementally creeping up on him.

The CNN poll shows a drop of 5 percentage points in support for Biden in the last three weeks, to 24 percent from 29 percent. The national survey of Democratic primary voters also saw Warren jump Sanders for second place, though the two are still within the margin of sampling error at 18 percent and 17 percent, respectively.

The latest numbers come a little over 24 hours before the top three contenders appear on the same debate stage for the first time in the primary contest. Thursday’s debate in Houston will, more specifically, feature Biden and Warren together for the first time, a dynamic that comes with more scrutiny as Warren continues her steady climb in the polls.

Wednesday’s survey shows an increasingly wide gap between the top tier of candidates and the rest of the field, despite three candidates dropping out of the race in recent weeks.

Sanders’ 17 percent is more than double the next-highest candidate, Sen. Kamala Harris, whose poll numbers have largely bottomed out after initially spiking following her takedown of Biden in the first debate. Harris pulled in 8 percent support, followed by another once-rising star, Mayor Pete Buttigieg of South Bend, Ind., with 6 percent, up from 5 percent for both candidates last month. Former Rep. Beto O’Rourke also rose 2 points in the poll, to 5 percent, while the remaining candidates polled at 2 percent or less.

But despite some erosion of Biden’s lead, the CNN poll also indicates that his campaign’s recent concerted efforts to sell their candidate as the most electable in the primary field might be boosted by voters’ determination to unseat President Donald Trump.

Four in 10 Democratic voters said that they wanted to see their party nominate a presidential candidate they agree with on major issues — the same as three weeks ago. But a majority, 55 percent, maintained that the party should prioritize nominating whichever candidate has a strong chance of ousting Trump from office.

The survey found a less drastic split among Democrats when it came to their concerns about the eventual nominee being on the wrong side of the ideological spectrum: 49 percent said they were worried the Democratic nominee would be too liberal, while 41 percent said they feared the party would nominate a candidate who was not liberal enough.

While Wednesday’s survey does meet the Democratic National Committee’s qualifying guidelines for the party’s primary debates, it holds no implications for next month’s debate because everyone meeting the 2 percent threshold has either already qualified or has reached 2 percent in an earlier CNN poll.

The CNN poll was conducted Sept. 5-9 among a total of 1,639 adults by telephone, including a subset of 908 registered Democratic and Democratic-leaning independents who are registered to vote. Results from the sample of Democratic voters have a margin of sampling error of plus or minus 4.3 percentage points.