Almost 30 percent of Biden supporters pick Sanders as second choice

Former Vice President Joe BidenJoe BidenThe Memo: Biden seeks revival in South Carolina Sanders makes the case against Biden ahead of SC primary Sanders holds 13-point lead in Fox News poll MORE (D) is atop the field of Democratic presidential candidates in most polls, but a new survey finds that many of his supporters would be willing to back his top rival, Sen. Bernie SandersBernie SandersBloomberg: 'I'm going to stay right to the bitter end' of Democratic primary race The Memo: Biden seeks revival in South Carolina Sanders makes the case against Biden ahead of SC primary MORE (I-Vt.).

A Hill-HarrisX poll released Wednesday found that 27 percent of registered voters who support Biden said Sanders was their second pick to become the Democratic nominee.

He was followed by Sen. Kamala HarrisKamala Devi HarrisThe Memo: Biden seeks revival in South Carolina Bloomberg campaign lobbied Yang for endorsement, possible VP offer: report Biden looks to shore up lead in SC MORE (D-Calif.), with 15 percent of Biden backers saying she was their second choice. Former Rep. Beto O'RourkeBeto O'RourkeCNN signs Andrew Yang as contributor Krystal Ball: Voters are coming to their own judgements about who is electable Warren campaign to host series of events in Texas MORE (D-Texas) garnered 11 percent and South Bend, Ind., Mayor Pete ButtigiegPeter (Pete) Paul ButtigiegBloomberg: 'I'm going to stay right to the bitter end' of Democratic primary race The Memo: Biden seeks revival in South Carolina Delegate count unchanged after Iowa caucus recount completed MORE (D) received 10 percent.

In the single digits were Sen. Elizabeth WarrenElizabeth Ann WarrenBloomberg: 'I'm going to stay right to the bitter end' of Democratic primary race The Memo: Biden seeks revival in South Carolina Sanders holds 13-point lead in Fox News poll MORE (D-Mass.), at 8 percent; Sen. Kirsten GillibrandKirsten GillibrandNow is the time for a US data protection agency The Hill's Campaign Report: Warren up, Bloomberg down after brutal debate Ginsburg, accepting lifetime achievement award, urges working fathers to take an active role in kids' lives MORE (D-N.Y.), with 7 percent; and Sen. Cory BookerCory Anthony BookerThe Memo: Biden seeks revival in South Carolina Bloomberg campaign lobbied Yang for endorsement, possible VP offer: report Warren calls for changes to presidential pardon power, pledges to create clemency board MORE (D-N.J.), at 6 percent.

Other polls have seen similar results.

An April 29-May 5 survey of 15,770 likely Democratic primary voters conducted by Morning Consult found that 31 percent of Biden supporters said Sanders was their backup choice. Harris was named by 13 percent, followed by Warren's 10 percent.

Before Biden entered the race, an April 12-15 poll from Change Research, a left-leaning group, found that Sanders gained 6 percentage points of support when the former vice president was excluded from the questionnaire seen by respondents. O'Rourke gained 5 points, while Buttigieg saw a 4-point increase.

An April 11-15 survey conducted by Monmouth University found that Sanders gained 7 points without Biden, with Harris and Warren each gaining 3 points.

The level of support among Biden backers for the further-left Sanders suggests Democratic voters don't neatly align in discrete demographic or ideological "lanes," Ruy Teixeira, a senior fellow at the Center for American Progress Action Fund, said Wednesday on Hill.TV's "What America's Thinking."

"The whole business with lanes can be quite exaggerated, particularly if we're thinking about the actual voters as opposed to the people analyzing the voters," he told host Jamal Simmons. "They have a more broad, more disparate sense of preferences, and the electability thing sort of gets plugged in there for a lot of Democrats who are sick of Trump."

To the extent that discrete groupings exist among dedicated party activists or large donors, the challenge for candidates seeking to dislodge Biden is to find a way to expand their appeal beyond their initial constituencies, Teixeira said.

"What you want to do is attract people across these so-called lanes," he said. "That's why Biden's doing so well at this point: He's taking people from all the lanes."

But expanding their support base may prove difficult with more than 20 contenders in the race, Republican pollster Ed Goeas told Simmons.

"American voters like to choose between two candidates," the veteran GOP strategist said.

"That is the one complicating factor you have now with Sanders and Biden both very high on name ID; they may be crowding out the second choice and certainly the data shows that's what's happening," Goeas said.

The Hill-HarrisX survey was conducted May 3-4 among 440 Democratic and independent voters who leaned toward the Democratic Party. The survey has a 95 percent confidence level and a 4.7 percent sampling margin of error.

The second choice analysis is based on a subset of 203 respondents who said Biden was their first choice. The sampling margin of error for the subset is 6.9 percent.

—Matthew Sheffield