Image copyright Getty Images Image caption Mr Sanders's supporters hope their candidate will deliver on the change they say Obama never delivered

On the eve of the Nevada caucuses, in an outdoor amphitheatre in a suburb of Las Vegas, Vermont Senator Bernie Sanders outlines to the crowd of several thousand the forces arrayed against his upstart presidential campaign.

"This campaign has taken on the big money interests in the economic establishment. We've taken on the political establishment, and we've taken on the media establishment," he said.

"And we're gaining ground every day."

For many in the audience, that "political establishment" includes the leader of their own party for the past seven years, Barack Obama.

Their disillusionment with a president who campaigned on hope and change eight years ago is palpable.

"He disappointed me," says Leslie Liston from Henderson, Nevada.

She says she supported Mr Obama in 2008 because of the groundbreaking nature of his being the first black US president, but her priorities have now shifted.

"I'm not just going to vote for someone to be the first of something, I'm going to vote for somebody because they know what they're talking about and they want to do the right thing," she said.

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Ms Liston said this was the first political rally she had ever attended - and Saturday will be the first time she has participated in the Nevada caucuses.

Others in the crowd, however, were veterans of the first Obama campaign in 2008 and painted a picture of a inspirational candidate who had gone astray once in power.

"Obama seemed to start with the right idea, motivating people, getting young people energised and activated to vote," said Debra Mayes of Los Angeles.

"Where he failed is not sustaining that movement. He just dropped the ball on that."

Sanders supporters focused on what they see as the shortcomings of the Obama administration, and of moderate Democrats beholden to their corporate donors.

The establishment Democrats, they said, essentially wasted the majorities the party had built during the years leading to Mr Obama's sweeping victory.

If Democratic leaders, including Mr Obama, had been more ambitious, they would have been able to establish a lasting congressional majority, the argument goes.

Media playback is unsupported on your device Media caption What does Bernie Sanders say in his stump speech? A 60 second summary of his greatest hits

"He was supposed to bring universal health care, and he just sacrificed that at the very beginning of the discussion," said Noah Neumark, who travelled from Los Angeles to help the Sanders campaign in Nevada.

"I know he had a lot of contention with the Republicans, but when you're negotiating you want to start from the high point."

Instead, he says, Mr Obama's election was a promise of change unfulfilled; a great hope dashed.

The Sanders fans in Nevada are not arriving at these views by chance, either.

In many ways they are reflecting the position of the man they spent Friday evening cheering.

Earlier this month during a television interview, Mr Sanders said that Mr Obama has been unable to provide the leadership to "close the gap" between the views of the American people and the actions of a conservative-dominated Congress.

"What we need, when I talk about a political revolution, is bringing millions and millions of people into the political process in a way that does not exist right now," Mr Sanders continued.

It is a revolution that some may have thought Mr Obama would usher in, instead of the progressive-tinted pragmatism that his presidency represented.

Image copyright Getty Images Image caption Mr Sanders met President Obama at the White House last month

Mr Sanders's disagreements with the president go back much farther than this current campaign.

In 2012 he repeatedly said that the nation would benefit from a progressive candidate challenging Mr Obama's re-election campaign in the party primaries.

"In a democracy, it's not a bad idea to have different voices out there," he said during an interview.

According to Patrick Caldwell of the progressive magazine Mother Jones, the Obama campaign even began preparing for a possible challenge from Mr Sanders.

That never materialised. But the Vermont senator gave only a tepid endorsement of Mr Obama during the general election, noting that the president "has not been as strong as he should standing up to Wall Street".

In the past few years Mr Sanders has opposed Obama-backed legislative priorities, including the Trans-Pacific Partnership (TPP) trade deal (which Mrs Clinton also now is against), government surveillance programmes and the president's budget compromises with congressional Republicans.

According to a report by CQ Weekly, Mr Sanders voted against Mr Obama's interests 17.5% of the time last year - more than all but four Democratic senators.

Image caption Grassroots support has been growing for Mr Sanders

Another strike against the president came in the form of a cover blurb, written by the senator, for a book titled Buyers' Remorse: How Obama Let the Progressives Down.

"Read this book," Mr Sanders urged.

What it all amounts to is a campaign for the Democratic nomination that is leavened with critiques of the sitting Democratic president - a man still immensely popular with many in the party.

That has created an opening for Mrs Clinton, who at the Democratic debate on 11 February went on the attack.

"The kind of criticism that we've heard from Senator Sanders about our president, I expect from Republicans," she said.

Mr Sanders replied that her attack was a "low blow" and that he has worked with Mr Obama in the past.

There is a bit of irony in Mrs Clinton's recent move to contrast herself with Mr Sanders as the heir to the Obama legacy.

Image copyright AP Image caption Mr Sanders won big in New Hampshire and hopes to do so again in Nevada

Just last autumn she seemed to be trying to do exactly the opposite - perhaps as a way of protecting her political left flank.

Mr Sanders' early success in Iowa and New Hampshire however has proved that strategy unsuccessful.

Now the former secretary of state needs help from those who still strongly support the president - particularly black voters.

In 2011, when Mr Sanders was musing about how someone on the left should challenge Mr Obama's re-election campaign, he gave a speech denouncing billionaire Wall Street crooks and a Democratic Party that was little different from the Republicans.

All these themes should sound familiar to anyone following the 2016 Democratic campaign.

Mr Sanders also had some advice for Mr Obama: "Fight for a progressive agenda, and do not equivocate," he said.

"You're not going to be able to win unless you're prepared to fight."

Now, looking ahead to what could be a long battle with Mrs Clinton for the Democratic nomination, it seems Mr Sanders is taking his own advice to heart.