This United States presidential election threatens to splinter the nation's two-party system, in place now for almost two centuries.

Bernie Sanders believes he can save the Democratic party from itself, a party he once called "politically bankrupt" and a "sham".

The eight years of the Obama administration has been a staring down and shouting match.

A stalemated Washington reflects an ever-deepening political void that is fuelled by the country's historic racial, geographical and social divides and by its current economic malaise.

Polls show that voters are sick of its national politicians, and this has launched the rise of two alleged outsiders, Donald Trump and Sanders.

Both the dubious billionaire and the maverick senator have reviled, defied and ridiculed the two major parties, whose banners they hoped to carry to the White House. Their successes have shaken the parties to the core.

A progressive army

Astoundingly, closed-rank Republicans have been the most virulent critics of Trump, the party's new mostly uncontrollable strongman and the champion of the suddenly disaffected.

And Hillary Clinton, who fought a political war to turn back the insurgent Sanders, is struggling to pull together a party that has always teetered on the brink of dissolution as a loose coalition of labour, minorities, progressives, centrists and younger voters.

Trump is good at quick labels, like "Crooked Hillary", but Sanders has been her most damaging political critic.

Sanders has made his intentions clear. He wants to re-imagine the Democratic party. He was to re-invigorate it with a progressive agenda that doesn't just mouth liberal ideals.

Though Sanders has been defeated for the Democratic nomination, the pugnacious former mayor remains a central figure in the campaign now little more than a month from the nominating conventions.

That he is 74, from a small, homogenous white state, that he is a socialist and a Jew, both previously toxic in national politics, and that he is not even a member of the party - none of this has been much of a hindrance. He has drawn millions of voters and small donors reacting to his call for a "political revolution".

So now, that he is out of the running for the nomination, what does Sanders want?

And how will his progressive army affect the election of the commander-in-chief of the world's most powerful military and the steward of a massive economy that impacts on the world with every twitch and stumble?

And will he be able to defy history and sustain his group of virulent supporters to change the party forever?

Clear intentions

Sanders has made his intentions clear. He wants to re-imagine the Democratic party. He was to re-invigorate it with a progressive agenda that doesn't just mouth liberal ideals.

He wants to lurch it forward from the centrist Clinton-Obama ideology to represent what he sees as the true desires of the people, particularly young people, a large part of his followers.

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In short he wants to keep his movement, his revolution, alive. Ross Perot couldn't do this with a third party run in 1996; Theodore Roosevelt couldn't in 1912 when he created the Progressive party after he lost the Republican nomination; and Ralph Nader faded after running as a third party candidate in 2000.

Unlike those three, Sanders wants to sustain a movement within one of the big two parties.

In the closest thing to a concession speech, without conceding, Sanders said last week: "I also look forward to working with Secretary Clinton to transform the Democratic Party so that it becomes a party of working people and young people, and not just wealthy campaign contributors."

The implication is that the party and Clinton have been for hire, dependent on big money donors, who dominate US politics.

In 2012, Obama and Mitt Romney raised a combined $2bn and this year that number is expected to rise, if Trump can close the fundraising gap.

Sanders' comment suggests that neither Clinton nor Obama - whose two elections were in large part a result of the very progressives that Sanders has rounded up - have led the party to the benefit of "working people and young people".

Clinton supporters are furious at Sanders. Traditionally, candidates who lose the nomination endorse the nominee and stand down, as Clinton herself did after losing a bitter race to Obama in 2008.

Sanders has been called a sexist, an egoist and an obstructionist.

Shaping the Democratic Party

Sanders forces now are zeroing in on the Democratic party platform, a working political agenda that is often discarded post-election.

The platforms are the result of intricate negotiations on the wording and direction of a list of priorities on a large range of issues.

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Sanders wants the party to adopt key positions he has raised on jobs, healthcare, racial justice, free college tuition, a more sceptical view of Israel in its relationship with Palestinians and regulation of the financial industry.

The negotiations are to be conducted with party officials that Sanders has heavily criticised. If there is to be a showdown at the Democratic convention in Philadelphia next month, it will be over the platform.

In the end, though, the platform will be a minor skirmish in the battle for the soul and direction of the party.

Sanders has his large group of committed voters as his leverage. Though history has shown that voting blocs are difficult to sustain to subsequent presidential elections, Sanders' David v Goliath campaign has given voice to a defiant group that wants to battle the Republican and Tea Party obstructionists with a can-do liberal populism.

Sanders wants to lead in the Democratic party from the outside. As an outlier, he has shocked this political campaign with unexpected success and proposes a revolution that promises to change US politics for generations.

If he makes that happen, losing to Clinton won't be his enduring legacy.

Lonnie Isabel is a reporter, editor and journalism instructor who has covered US politics and foreign affairs for three decades.

The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial policy.