After four months of campaigning, the Democratic presidential race remains wide open, with the bulk of the electorate still uncommitted, according to a Washington Post-ABC News poll.

Asked to name the candidate they currently support, 54 percent of Democrats and Democratic-leaning independents did not volunteer anyone. That figure is little changed from 56 percent in January, despite a slew of candidate announcements, vigorous campaigning in the early primary and caucus states, multiple cable television town halls and interviews and constant fundraising appeals.

Among the minority who expressed a preference, former vice president Joe Biden holds a tenuous advantage over Sen. Bernie Sanders (I-Vt.).

At least 20 contenders are courting a Democratic electorate closely divided over whether to nominate someone who can energize the party’s core constituencies or win over political independents.

Biden’s campaign is centered on the idea of being the most likely to defeat President Trump in a general election. But slightly more Democrats and Democratic-leaning adults prefer a candidate whose positions are closest to theirs, rather than the one who seems most electable.

Democratic candidates have played to big and enthusiastic audiences in Iowa, New Hampshire and South Carolina. But the high and persistent level of uncertainty suggests that many Democratic voters are cons idering multiple options or have yet to pay much attention nine months before the Iowa caucuses. It also indicates that support for most candidates is more tenuous than suggested by surveys that ask respondents to choose among the lengthy list of Democratic contenders.

Former vice president Joe Biden announced his bid for president on April 25. Here's a look at the two other times he ran for president. (Monica Akhtar/The Washington Post)

The Post-ABC poll, conducted largely before Biden’s Thursday campaign announcement, asked whom respondents support in an open-ended format that did not name any of the candidates. The results show notably lower levels of support than produced in polls that ask people to pick from a list of names.

Biden tops the field with 13 percent among Democrats and Democratic-leaning adults, followed by Sanders at 9 percent and South Bend, Ind., Mayor Pete Buttigieg at 5 percent. Sens. Kamala D. Harris (Calif.) and Elizabeth Warren (Mass.) are at 4 percent, while former congressman Beto O’Rourke of Texas is at 3 percent. Sens. Amy Klobuchar (Minn.) and Cory Booker (N.J.) are at 1 percent each.

Support for Biden has ticked up four percentage points since a Post-ABC poll in January that used the same open-ended format. Sanders gained five points in that time, as has Buttigieg, whose name was not volunteered by any respondents three months ago. Support for Harris has dipped four points from January.

The poll finds less than 1 percent of Democratic-leaning adults volunteering former Colorado governor John Hickenlooper, former San Antonio mayor Julián Castro and entrepreneur Andrew Yang. None of the survey’s 427 Democratic and Democratic-leaning respondents volunteered Rep. John Delaney (Md.), Sen. Kirsten Gillibrand (N.Y.), Gov. Jay Inslee (Wash.), Rep. Seth Moulton (Mass.), Rep. Tim Ryan (Ohio), Rep. Eric Swalwell (Calif.) or author Marianne Williamson.

Biden has a clearer advantage over Sanders when taking into account a follow-up question asking which candidate Democrats lean toward, which still did not name candidates. The poll finds 17 percent support or are leaning toward Biden, compared with 11 percent for Sanders, 5 percent for Buttigieg and 4 percent each for Harris, Warren and O’Rourke. No other candidate breaks 2 percent.

Biden benefits from double-digit support among a wide range of Democratic and political groups, when taking into account both initial support and respondents’ leanings. He garners 19 percent support among moderate-to-conservative Democrats, and 13 percent among self-identified liberals, just slightly behind Sanders’s 16 percent in that latter group. Biden receives similar levels of support among whites and nonwhites, as well as among rank-and-file Democrats and independents who lean toward the party.

Biden receives 18 percent support among men and 16 percent among women, who make up a clear majority of Democratic voters. Biden has been criticized recently by several women who said he made them uncomfortable with hugs or other physical expressions of affection. He has said he recognizes that in the #MeToo era, he must be more respectful.

Younger Democrats are a clear weak spot for Biden, with 7 percent of those under age 40 expressing support for his candidacy. That compares with 24 percent support among Democratic-leaning adults ages 40-64 and 25 percent support among seniors.

Sanders’s support is fairly even across the primary electorate in this Post-ABC poll. He receives a similar level of support among whites and nonwhites, as well as among college graduates and those without four-year degrees, and among those with higher and lower incomes.

But Sanders, among the progressive candidates in the Democratic field, receives 16 percent among liberals compared with 8 percent among moderate-to-conservative Democrats. He also receives twice as much support from independents who lean Democratic vs. rank-and-file Democrats, echoing a pattern from his 2016 campaign.

Sanders’s 2016 strength among younger adults continues. He has the support of 14 percent of Democratic leaners under age 40, though he also receives 12 percent support among those ages 40-64. He receives just 4 percent support among seniors.

Buttigieg’s 5 percent support is spread fairly evenly across demographic groups, with the exception of education and race: 10 percent of college graduates support him compared with 3 percent of those without four-year degrees. And while 8 percent of white Democratic leaners back Buttigieg, that falls to 3 percent among nonwhites.

The Post-ABC poll finds stark demographic and political divides in which Democrats have chosen a favorite candidate so far, an indication of how some highly engaged groups are driving early vote preferences while the influence of others may not be seen until closer to the primary contests.

Education is a principal divide. In the open-ended question, 61 percent of college graduates volunteer support for a candidate. That compares with 35 percent of Democratic-leaners without college degrees. Liberals are 17 points more likely to name a candidate at this stage than are moderate or conservative Democrats. Men are 15 points more likely to name a candidate at this stage than are women. Race and age also factor in, with whites and Democrats 40 and older more likely to state support for a candidate.

As the Democratic electorate pays more attention, it appears divided over which political traits are most important in a party standard-bearer. Asked to choose which is more important, 48 percent say they prefer a candidate who is best positioned to energize the Democratic base, while 44 percent prefer a candidate who can best win over independent voters.

A separate question finds about 4 in 10 Democratic-leaning adults saying it is more important to choose a candidate who seems most likely to defeat Trump in the general election, though slightly more say they should choose the candidate whose issue positions are closest to theirs. Both findings suggest ample room for candidates to appeal to voters on policy issues and on the question of electability in the coming months.

The Post-ABC poll was conducted by telephone April 22-25 among a random national sample of 1,001 adults, with 65 percent reached on cellphones and 35 percent on landlines. The margin of sampling error among 427 Democrats and Democratic-leaning independents is plus or minus 5.5 percentage points.

Emily Guskin contributed to this report.