WASHINGTON — President Obama turned his back on the millions who rallied to support him when he assumed office, cutting off the only means he had to effect the sweeping changes he promised on the campaign trail in 2008 and leaving him at the mercy of Republicans in Congress.

That's the diagnosis from Bernie Sanders, the independent Vermont senator and Democratic presidential candidate who held court as the left-wing attack dog in the presidential race for about an hour Thursday surrounded by reporters at one of Washington's fanciest hotels.

Sanders proclaimed himself the man with the "most progressive views of any candidate" in the race — "philosophically, I am a Democratic Socialist," he said at one point — and proceeded to prove the point, detailing broad support for western European economic and education policy, attacking Democratic frontrunner Hillary Clinton for declining to publicly join the progressive push against free trade expansion, bemoaning money in politics while also promising never to have his own super PAC and proudly noting he never voted for any of the U.S. wars in Iraq, including the one launched in 1991.

He spoke about how the faith he was born into motivates him, addressed a weird interview with public radio in which he was accused of having joint US-Israeli citizenship, and spoke about his surprising success in the nascent days of his presidential bid.

The impassioned critique of Obama summarized Sanders' skill at vocalizing the frustrations of the president's progressive allies, laying out succinctly what anyone who has been within distant earshot of a progressive activist has heard many times.

"The biggest mistake Barack Obama made in my view is that after his brilliant campaign in 2008 where he mobilized millions of people, ran one of the great campaigns in American history, essentially what he said to his supporters was, 'thank you very much for electing me, I'll take it from here on myself. I'll sit down with John Boehner, I'll sit down with Mitch McConnell, we'll negotiate, we'll come up with some compromises, thanks very much for what you did,'" Sanders said. "I will not make that mistake. The point that I'm making is, and this is where my campaign is very different from the others, I do not believe that any president who is standing up for the working class of this country can be successful without the mobilized activist grassroots movement behind him or her. So I will be working hard to make sure that mobilization exists."

As for Clinton, Sanders expressed bewilderment that the former Secretary of State hasn't publicly chosen sides in the trade debate with hours to go before a House vote on fast-track trade authority that the activist left has made defeating as its number one goal.

"You can be for the [Trans-Pacific Partnership trade deal], I think the president is dead wrong, he is for it," Sanders said. "You can be against it, I'm against it, Warren's against it, Sherrod Brown's against it, the majority of Democrats in the Senate are against it. You can be for it, or against it. I don't understand how on an issue of such huge consequence, you don't have an opinion."

Clinton has been playing it very cautiously on the president's trade agenda, avoiding directly pitting herself against either Obama or his progressive opponents.

"There are questions being raised about this agreement. It hasn't been negotiated yet," Clinton said on the trail in Iowa recently. "I have said I want to judge the final agreement."

Sanders also spoke of big marches on Washington by students demanding a better deal on college costs and marches by workers demanding an increase in the minimum wage.

Sanders' Obama history is a little off, though his tactical critiques are often raised by liberals. Obama turned his campaign into first Organizing for America and then Organizing For Action, nonprofits whose goal in part was to keep Obama's campaign infrastructure in place for the reelect but also to use his massive list of supporters to pressure Congress via online campaigns and public rallies. Large OFA marches and rallies, feared by some of Obama's opponents after he won in 2008, never really materialized, although digital campaigns in support of the president's policies are still blasted out of OFA's Chicago headquarters on a regular basis.

Sanders has done well in his opening weeks as a candidate, amassing, he said, more than 200,000 small-dollar donors and racking up poll numbers that make him number two in the Democratic nomination contest, albeit one running far behind the frontrunner Clinton. Sanders said he's in it to win it, and promised an increase in poll numbers as his name ID increases. He also promised to be outpspent by the impressive financial operations of Clinton. On the whole, he was comfortable in the role of pugnacious underdog, dismissing the Democratic Party's plan for primary debates and promising to open discussions with the party chair and his fellow candidates about how best to build a debate calendar.

The Washington event, a breakfast sponsored by the Christian Science Monitor, came just a day after Sanders' appearance on the Diane Rehm Show, a syndicated public radio program. Sanders said he forgave Rehm for her question about joint Israeli-American citizenship, a longstanding and wholly incorrect conspiracy theory labeled anti-Semitic by some Jewish groups in the hours after Rehm's broadcast.

"I like Diane Rehm. She is a good radio interviewer," he said. "I suspect what happens is her staff gives her a list of questions and someone screwed up pretty bad."

Sanders was asked to weigh in on how his relationship with Judaism affects his political outlook.

"I'm proud to be Jewish, I'm not particularly religious," he said. He said growing up Jewish in the post-World War II years taught him elections like the one that put Adolf Hitler in office can have very serious consequences.

"The lesson that I learned as a little kid was to understand in a very deep way what politics is about," he said.

Reporters also wanted to know a lot about Sanders' opinion of Europe. Sanders has long called for Western European-style social safety nets, universal healthcare programs, and structures that make higher education free or next to free for most students. America has a lot to learn from Europe, Sanders said. A reporter asked if he thinks Europe has much to learn from America.

"As a former mayor, what mayors look at is the concept of best practice. What best practices means…you look all over the country and you say, 'what are other cities doing that would be good?' and you steal those ideas," he said. "That's what we should be doing as a world. Are we doing things better than other countries? Of course we are, we have a lot to be proud of. We are a very entrepreneurial country, I mean every other day someone is coming up with another great idea, another great invention. We do that probably better than any other country on earth, and people should learn from us."

But in terms of protecting and taking care of the needs of working people," Sanders continued, "we have a lot to learn from many other countries around the world."

Sanders promised to bring many of those western European-style programs to the United States if he becomes president. Dinging the president again, Sanders said it was time for a more progressive approach than Obamacare.

Sanders seemed pleased by his growing standing as the Democratic Party's progressive-in-chief, a position fueled by a campaign that has lit up the grassroots on the left despite the lack of initial support from many activist left organizations who were until recently pouring all their efforts into trying to cajole Massachusetts Sen. Elizabeth Warren into the presidential race. His campaign building steam, Sanders, said he's been amazed by the DC money machine he's discovered as he's emerged as a prominent presidential candidate.

"A lot of people want to make a lot of money off of campaigns," Sanders said, when asked what he has learned so far. "There is an entire industry here in Washington, D.C. of folks who are prepared to help you for some extravagant fees."