Could Biden be forced out as election nominee and how might that work?

Joe Biden's stumbling performance in the US presidential debate has sparked alarm among Democrats - but could he be replaced against his will and how might that work?

Pic: AP

A national US party has never tried to force an election candidate to step down in the modern era and their rules make it almost impossible to do so.

The issue came before both parties in 2016, but neither took action and there's currently no known effort to force Mr Biden to give way.

It would mean Democrat officials overturning the results of the state primaries - the votes that took place earlier this year that confirmed Mr Biden as the overwhelming pick for November's election.

The 80-year-old won virtually all the delegates - and they are now set to go through the customary process of rubberstamping his nomination at the Democratic National Convention on 19 August.

There are ways to replace a nominee if they die, resign or are incapacitated, but forcing Mr Biden out would mean delegates choosing another candidate.

It appears highly unlikely, as they were chosen in the primaries because of their loyalty to the president and with the trust that they would vote for him at the convention.

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However, there is a potential "loophole" in that Democrat rules allow them to "in all good conscience reflect the sentiments of those who elected them".

So if concerns about his performance and mental acuity reach critical level this could be a way forward.

What if Biden withdraws himself?

This is the only plausible scenario for the Democrats to choose a new candidate to take on Donald Trump.

Mr Biden has repeatedly dismissed this option during other turbulent times, but if he changed his mind he could simply serve out the remaining months of his presidency.

Such a U-turn would create a frenzy among Democrats as there's no protocol in place for him or the Democrats to choose a new candidate before August's convention.

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It takes a majority of the party's 4,000 or so delegates to win the presidential nomination - and Mr Biden secured about 3,900 of them in the primaries.

Mr Biden would have some influence over his pledged delegates, but ultimately they can vote as they please - so candidates would most likely campaign aggressively to win them over.

If the president decides to call it quits after the convention takes place, the chair of the party can call a special meeting of around 500 members.

They can - in theory - choose a new nominee via a simple majority vote.

However, such a process would likely be far more turbulent, with behind-the-scenes jockeying and public campaigning.

If Mr Biden pulled out even closer to the 5 November election, it could raise constitutional, legal and practical concerns.

For example, voting papers have to be printed well in advance and it might not be possible to change them in time.

Would vice president Kamala Harris replace Biden?

If Mr Biden were to resign immediately as president, Kamala Harris would automatically succeed him - but would not also become Democratic nominee.

She might be politically favoured if he ditched his re-election bid, but Mr Biden's delegates would not automatically transfer to her and it would be a level playing field with other hopefuls.