Amid new signs of danger for President Trump’s reelection hopes, the opposition race to replace him is wide open, with most Democratic voters not able to name their favorite candidate, according to a new Washington Post-ABC News poll.

When asked whom they would support today for the Democratic presidential nomination, 56 percent of self-identified Democrats or Democratic-leaning independents did not offer a name. No candidate received double-digit support, with former vice president Joe Biden and Sen. Kamala D. Harris (D-Calif.) leading the pack.

The lack of commitment on the Democratic side comes as Trump appears vulnerable to defeat in a 2020 general election and perhaps even to a challenge from within the Republican Party.

A 56 percent majority of all Americans say they would “definitely not vote for him” should Trump become the Republican nominee, while 14 percent say they would consider voting for him and 28 percent would definitely vote for him. Majorities of independents (59 percent), women (64 percent) and suburbanites (56 percent) rule out supporting Trump for a second term.

Trump on Tuesday dismissed concerns about public opposition to his reelection. “That’s a much better number than I had in 2016. I think it’s going to change very easily,” he said in an interview with The Post. “I think we are going to do very well.”

Across six polls during President Barack Obama’s first term, between 41 percent and 46 percent said they would “definitely not vote for him.” That includes an October 2011 poll in which Obama’s approval rating sank to 42 percent, with disapproval at 54 percent. Obama won reelection in 2012 with 51 percent of the popular vote compared with Republican nominee Mitt Romney’s 47 percent.

While 75 percent of Republicans and GOP-leaning independents approve of Trump’s performance in office when asked separately, nearly 1 in 3 say they would like to nominate someone other than Trump to be the party’s candidate for president.

That weakness for Trump has encouraged Republicans such as former Ohio governor John Kasich and Maryland Gov. Larry Hogan, who have left open the possibility of challenging Trump in the GOP primary. Former Starbucks chief executive Howard Schultz is also considering an independent campaign for president based on the idea that he would draw support from Trump and the Democratic nominee.

Concerns over Trump’s reelection prospects were one of the reasons the Republican National Committee voted unanimously Friday for a resolution of “undivided support” for Trump and his presidency. The resolution stopped short of endorsing his reelection, as some on the committee had urged, largely because of legal concerns.

That did not stop Trump from falsely tweeting Saturday that the committee had voted “to support me in the upcoming 2020 Election.”

Among Democratic-leaning voters, indecision reigns after a flurry of candidate announcements in recent weeks. When asked an open-ended question about whom they would support if the election were today, 43 percent said they do not have an opinion. Seven percent said they would choose no one, with 5 percent saying any one of the Democratic candidates and 1 percent supporting “someone new.”

Biden was the person most often chosen, by 9 percent of Democratic-leaning voters, followed by Harris, with 8 percent, each garnering more support than any other named candidate. Sen. Bernie Sanders (I-Vt.) and Trump were named by 4 percent, followed by former congressman Beto O’Rourke (D-Tex.) with 3 percent.

Former first lady Michelle Obama and Sen. Elizabeth Warren (D-Mass.) each got 2 percent. Five other politicians and the media mogul Oprah Winfrey were named by 1 percent of respondents. Obama and Winfrey have said they are not seeking the office.

The views, and the absence of loyalty to a particular candidate, were consistent through a range of demographic groups. Biden is slightly more popular among older voters, while Harris, who announced her presidential campaign while the poll was being taken, has a minimal edge among college graduates.

College graduates are more tuned in to the primary fight, with 52 percent volunteering preference for a candidate. Sixteen percent volunteer Harris, while 10 percent volunteer Biden. A smaller 39 percent of Democrats with some college or less formal education named a candidate they support.

Democrats are also divided on the issues that are most important to them and the qualities they most look for in a candidate. Forty-seven percent of Democratic leaners say it is more important that the party nominate someone whose positions on issues are close to their own, compared with 43 percent who say they prioritize finding a candidate “most likely to defeat Trump.”

Democratic women are 11 points more likely than men to say it is most important to nominate a candidate with the best chance of defeating Trump, reflecting their continuing animosity toward the president. (Almost two-thirds of all women said they would definitely not vote for Trump, compared with 48 percent of men).

Just over half of liberal Democrats say the ability to defeat Trump is a more important candidate quality, 52 percent, compared with 37 percent of moderate and conservative Democrats.

Democrats also are divided over the issue that was most important to them. When given a list of four options, 31 percent said “improving the health-care system,” 21 percent said “reducing economic inequality,” 18 percent said “reducing racial and gender discrimination” and 15 percent said “combating global warming.”

Older Democrats put a greater priority on health care as an issue, while younger ones are more likely than seniors to prioritize economic inequality and global warming. Liberals and white Democrats are more likely to prioritize global warming. Nonwhite Democrats are more likely to prioritize reducing gender and racial discrimination.

The Post-ABC poll was conducted Jan. 21 to 24 among a random national sample of 1,001 adults, with 65 percent reached on cellphones and 35 percent on landlines. Overall results have a 3.5-percentage-point margin of sampling error. The error margin is plus or minus 5.5 points among the samples of 447 Democrats and Democratic-leaning independents and 405 Republicans and Republican-leaning independents.

Michael Kranish contributed to this report.