Right now there are only three candidates in the race. Biden is in first place, and Warren and Sanders share second place. Biden’s numbers have been steadily dropping, but I suspect he will experience a more dramatic drop over the next polling cycle or two. Sanders’ have been slowly dropping, and Warren’s numbers are going up at a somewhat faster rate than Sanders have been going down. In the chart below you can see them close to convergence in about 20 days now, given current trends.
Of course, the debate will shake all this up and possibly add or remove individuals from this top three spot.