The chart above reflects the results of the latest CNN / SSRS Poll -- done between March 14th and 17th of a national sample of 456 Democrats and Democrat-leaning Independents, and has a margin of error of 5.7 points.
Joe Biden hasn't officially entered the Democratic race for the presidential nomination, but he maintains a significant lead over the other candidates. I think this is because he is seen as the most likely candidate to beat Trump in the general election. Four other candidates also have significant support -- Bernie Sanders, Kamala Harris, Beto O'Rourke, and Elizabeth Warren.
None of the other candidates reach the 5% mark.
The chart below is the latest Economist / YouGov Poll -- done between March 17th and 19th of 1,287 registered voters, with a 2.8 point margin of error.
They asked a different question -- Do you have a favorable opinion of the Democratic candidates? Only six candidates had a majority of Democrats with a favorable opinion of them -- Biden, Sanders, Warren, Harris, O'Rourke, and Booker. No one else did better than 39%. And only one candidate had a majority of registered voters viewing him favorably -- Joe Biden.
There is still plenty of time for candidates to improve these numbers.