With some Democrats unsure of a Biden candidacy, what are the chances of a brokered convention?

Dogged by low approval ratings and concerns about his age, health and mental acuity, U.S. President Joe Biden continues to face concerns from some Democrats about his electability for a second term in office.

These concerns were more recently fuelled by a damning report from a U.S Justice Department special counsel over his handling of classified documents. The report referred to Biden as a "well-meaning, elderly man with a poor memory" who also suffered from  "diminished faculties." And for some Democrats, his subsequent news conference didn't help allay those fears.

Those fears have also sparked much speculation about whether Biden could be replaced as the party's nominee at this point. He is facing little opposition in the primary contest, meaning he is almost guaranteed to have secured the majority of delegates needed headed into the Chicago convention this August.

But the idea of a possible replacement is gaining more traction following a New York Times audio essay by journalist Ezra Klein. The essay, titled "Democrats Have a Better Option Than Biden" suggests that party leaders need to convince Biden to step aside, and allow for a brokered convention.

That would mean, with Biden no longer a candidate, Democratic delegates at the convention would choose a new leader to face off against the Republican nominee, who at this point will almost certainly be former president Donald Trump.

But just how likely will this happen? Not very, say political observers.

Those hoping some latecomer Democrat could still swoop in and challenge Biden in the primaries are out of luck, says Caitlin Jewitt, an associate political science professor at Virginia Tech, whose focus includes U.S.presidential primaries and caucuses.

At this point in the race, the filing deadlines to become a candidate have passed in more than 80 per cent of the states.

That means "there is no mathematical way that another candidate can enter the primaries and secure a majority of delegates and become the nominee," she said.

The delegates Biden racks up during the state primaries will cast their votes for him at the Chicago convention during what is essentially a state-by-state roll call. With Biden having run virtually unopposed, and having attained the majority of delegates needed, this is when he would be officially declared the party's presidential candidate.

If Biden decided at the convention that for whatever reason, he is not going to run in this year's election, then, yes, Klein's idea of a brokered convention would come into play. 

"They basically do multiple ballots at the convention until a candidate gets 50 per cent plus one," Jewitt said.

Names that have been bandied around include people like Vice-President Kamala Harris, California Gov. Gavin Newsom, Michigan Gov. Gretchen Whitmer or New Jersey Sen. Cory Booker.

If Biden decided to end his campaign today, the party's nominee would still have to be decided by ballot at the convention, because, with nominations only open in a handful of states, there are not enough delegates in those states for any new candidate to get the majority needed.