Hillary Clinton remains the Democratic frontunner, with 42 percent of Democratic support, down 10 percentage points from a month ago, according to a new national poll by Monmouth University.

And Vice President Joe Biden, who has not yet announced whether he will seek the Democratic nomination, has caught up to Bernie Sanders. Biden, at 22 percent, and Sanders, at 20 percent, are now virtually tied. And a majority of those Democrats or Democratic-leaning voters who currently support Clinton (56 percent) and Sanders (also 56 percent) say they'd be at least somewhat likely to think about throwing their support to Biden instead, if he were to decide to run.

Both Biden and Clinton have 71 percent favorable ratings, while Bernie Sanders has a 41 percent favorable rating. However, there are still 45 percent of Democrats who have no opinion to him - this shows little change from his rating last month.

Martin O'Malley and Jim Webb each have one percent of the Democratic vote. Not a single respondent chose Lincoln Chafee. Comedian Conan O'Brien launched an effort on his show last month to boost Chafee to one percent support, but he has so far failed. Then again, O'Brien also said, "Let's be honest, I'm not trying to get him elected, okay? In fact, I'm personally not going to vote for him. But I think we should at least get him on the board so he's at least not humiliated, seems like the nice thing to do."

The Monmouth University Poll was sponsored and conducted by the Monmouth University Polling Institute from August 31 to September 2, 2015 with a national random sample of 1,009 adults age 18 and older. This includes 707 contacted by a live interviewer on a landline telephone and 302 contacted by a live interviewer on a cell phone, in English. The results in this poll release are based on a subsample of 339 registered voters who identify themselves as Democrats or lean toward the Democratic Party.