The pool of Democrats vying for the nomination is one of the largest in recent memory, with 10 candidates itching to take on Trump in November 2020, Xinhua news agency.
In the lead is Biden, followed by Sanders and Warren.
California Senator Kamala Harris, who is of Indian and Jamaican descent, is at the top of the list of those who could conceivably overtake the current top three, followed by South Bend, Indiana, Mayor Pete Buttigieg.
However, the top three candidates have a number of hurdles to overcome, according to political analysts.
For Biden, his biggest problem is the fact that he is in his mid-70s. Many younger Democratic voters would prefer a younger candidate and a fresher face, rather than someone who already spent eight years in the White House.
The former Vice President is also particularly prone to gaffes, which appear to be catching up with him, as a number of news outlets have highlighted a few tall tales he told last week.
One, about being shot at in Iraq, turned out not to be true, as was another embellishment, that he marched in the US Civil Rights Movement an iconic movement in American history to promote equal rights for African Americans. That story also turned out to be untrue, reported US media.
Moreover, many believe Biden lacks the ability to inspire, which endeared former President Barack Obama to his supporters. Those who support Biden do so because of his policies and the fact that he could, they believe, unseat Trump, the analysts added.
At the same time, many believe that Biden is the only Democratic candidate with a chance of beating Trump in 2020. And some experts believe that factor alone will cause voters to cast their ballots for him in the Democratic primaries.
Meanwhile, critics describe Sanders and Warren as "unelectable". Sanders is pushing a green energy plan that some US media have dismissed as laughable.
The plan would cost $16 trillion, and entirely end the use of fossil fuels. It has been called a "fantasy".
Sanders has also indicated the possibility of criminal prosecution of oil, gas and coal executives. The plan has been dismissed as simply not serious.
For her part, Warren has espoused policies such as a wealth tax and universal child care, which critics said are admirable but unworkable.
Virtually all the Democratic candidates have pushed for increased taxes on the wealthy, such as taxing their assets instead of just their incomes.
The party next debate will take place on September 12 in Houston, Texas.
( With inputs from IANS )