Former vice president Joe Biden and Senator Bernie Sanders lead the field of Democratic presidential candidates, followed by SenatorElizabeth Warren, according to a nationwide NPR/PBS NewsHour/Marist poll released Monday.

The poll of Democratic and Democratic-leaning independents shows Biden with 24% support and Sanders at 22%, within the margin of error of 5.4 percentage points. Warren had 17%, and Pete Buttigieg had 13%. None of the other candidates scored above 5%.

The poll, released before a debate of Democratic candidates on Thursday, shows a very fluid field, with 76% of Democratic and Democratic-leaning respondents saying they could change their minds about the contender they favor.