(CNN) President Donald Trump is attacking it. Moderate Democratic candidates are warning against it, too. But in a speech Wednesday, Sen. Bernie Sanders leaned in to his democratic socialist vision, casting his policies as the "unfinished business" of the New Deal era, and argued that the nation must embrace his politics in order to defeat rising global authoritarianism.

"It is my very strong belief that the United States must reject that path of hatred and divisiveness and instead find the moral conviction to choose a different path, a higher path, a path of compassion, justice and love," Sanders said to applause at George Washington University. "And that is the path that I call democratic socialism."

Over nearly 45 minutes, Sanders quoted in his defense a range of historical figures, from Presidents Franklin Delano Roosevelt and Harry Truman to Dr. Martin Luther King Jr. He also recalled comments from figures like President Ronald Reagan, who during his pre-White House days served as a go-to spokesman for conservatives and used "socialism" as a slur against an assortment of liberal policy projects, including now popular programs like Medicare.

Sanders also took aim at Trump, calling him a friend of "corporate socialism" and the American face of an international "movement toward oligarchy (that) runs parallel to the growth of authoritarian regimes."

Sanders' speech, which echoed in parts a similar address he gave during his last presidential campaign, came amid a growing backlash, from both Republicans and some Democrats, to his unlikely rise into the upper echelons of American politics. He began the 2016 Democratic presidential primary as a relative unknown, a Senate backbencher generally viewed -- even by himself -- as an outsider inside the Washington beltway. But his message gained traction when pitted against eventual nominee Hillary Clinton, a pragmatism-preaching liberal who was ultimately defeated, in part, by Trump's right-wing populist appeal.

Sanders entered the 2020 race offering much the same message as four years ago, but with loftier electoral expectations and a more mature political operation. He also, now, has a more useful foil when it comes time to defend his agenda -- the Trump administration.

"When Trump screams socialism, all of his hypocrisy will not be lost on the American people," Sanders said Wednesday. "When Trump attacks socialism, I am reminded again of what Dr. Martin Luther King, Jr. said: 'This country has socialism for the rich; rugged individualism for the poor.'"

Sanders described Trump, Wall Street and other powerful corporations as a common enemy lined up against the shared interests of the working and middle classes -- and dismissed criticism coming from the President and his allies as transparently self-serving and insincere.

"While President Trump and his fellow oligarchs attack us for our support of democratic socialism, they don't really oppose all forms of socialism," Sanders said. "They may hate democratic socialism because it benefits working people, but they absolutely love corporate socialism that enriches Trump and other billionaires."

Promising to continue to roll out new proposals to complement his signature "Medicare for All," single-payer health care plan, Sanders also described a coming "21st century Economic Bill of Rights" -- a new version at what Roosevelt first spoke about in the year before his death.

"A Bill of Rights," he said, "that establishes once and for all that every American, regardless of his or her income is entitled to the right to a decent job that pays a living wage; the right to quality health care; the right to a complete education; the right to affordable housing, the right to a clean environment; and the right to a secure retirement."

In the run-up to the speech, Sanders campaign manager Faiz Shakir sought to separate out Sanders' argument from other candidates in the Democratic primary, most notably -- though without saying his name -- former Vice President Joe Biden.

"There is this belief that technocratic squishiness is the way to solve problems," Shakir told CNN. "Sen. Sanders is prepared to make the argument that what we need is a fighter unafraid to take on the big problems of the day and offer up real solutions to solve them."

Shakir conceded that the "socialism" label is one that Sanders' opponents -- both Democrats and Republicans -- will continue to use in an attempt to tar his campaign, but insisted the Vermont senator would never back off his fundamental argument.

"This is a fight we are excited to have," Shakir said, denying the speech was a response to dipping poll numbers or an attempt to reboot the campaign. "We are not going to duck this charge. We plan to take it on front and center. This has always been something that (Sanders') political opponents have used as a way to try and bring him down and despite those attacks, he has only gotten more popular."

In a video posted Wednesday morning, Florida Republican Sen. Marco Rubio gave a glimpse at the response Sanders can expect from political rivals. He called democratic socialism a "trendy phrase" used by the "radical left to ignore the incredibly destructive history of socialism," and declared it "incompatible with our American values."

The wider public response to Sanders' words will be watched closely not only by his political rivals, but by leaders of the Democratic Socialists of America, which has grown into the country's largest socialist organization -- with 56,000 dues-paying members -- in the wake of Trump's 2016 election. Its stars, like New York Rep. Alexandria Ocasio-Cortez, have used their megaphones to reshape public perception around socialism -- which has for so long been viewed as a dirty word in national politics.

Ocasio-Cortez was put on the spot soon after her surprise primary victory last year, when she was asked during an appearance on "The Late Show with Stephen Colbert" what democratic socialism meant to her.

"I believe that in a modern, moral and wealthy society, no person in America should be too poor to live," Ocasio-Cortez said in a clip that almost immediately went viral. "So what that means is health care as a human right. It means that every child, no matter where you are born, should have access to a college or trade school education if they so choose it ... I think that no person should be homeless if we can have public structures and public policies to allow for people to have homes and food and lead a dignified life in the United States."

Support for socialism can be tricky to measure through public polling. Democrats generally have a more favorable view than Republicans , but its support has not risen along with Sanders' political fortunes. Policies rooted in socialism, like Medicare or social security are widely popular across political lines. Another consistent finding has been diminished backing for capitalism, especially among young people and Democrats. According to a Gallup poll from last year, support for capitalism among 18- to 29-year-olds had fallen more than 20 percentage points over eight years, from 68% to 45% in 2018. But there was no movement when it came to socialism -- it stood at 51% in both 2010 and 2018.

Whether a modern candidate who embraces socialism can win a presidential election remains an open question. In another Gallup poll from April, fewer than half of Americans (47%) said they would vote for a candidate nominated by their party who is "a generally well-qualified person for president who happened to be a socialist." It was the lowest figure among a range of traits tested, including being "a woman" (94%), "a Muslim" (66%) or "an atheist" (60%). But candidates, like Sanders, are not so easily categorized. He is also Jewish (93%) and over 70 (63%).

With Ocasio-Cortez's victory, and the march of other unabashed democratic socialist candidates at all levels of government, the term has come under increasing scrutiny -- both from Republican opponents and Democrats who either disagree ideologically or worry that the label looks like a political skull and bones to voters. Recent rhetoric from both parties has created a sense that socialism itself is on the ballot -- or on trial -- in this campaign.

But Maria Svart, DSA's national director, believes Sanders' popularity and changes to the broader political discourse, headlined by growing income inequality and a sharp rise in concerns over climate change, has changed the context of the debate.

"Capitalism is what's on trial," Svart told CNN before the speech. "This is not a drill. This is absolutely our last chance to change our system. The United States is the biggest polluter on the planet. Trump is actively making it easier to pollute. And if we don't stop it, we don't have a future."

Like the Sanders campaign, which DSA voted to endorse, Svart also argued Democrats desperate to defeat Trump in 2020 needed to embrace a more radical political agenda.

"(Sanders) is giving this speech at a time when Trump, and certainly the Republicans, have a unified talking point that all Democrats are socialists. And obviously I wish that were so, but we've seen the narrative around Biden and others about electability, and the reality is that too many Wall Street Democrats are completely out of touch with millions of people in this country," Svart said, adding that Sanders' "central argument needs to be that socialism works for the 99%, socialism works for the many, and we should be more socialist. There is no alternative if we want to beat Trump."

Centrist and more cautious liberal Democrats on the campaign trail have become increasingly vocal -- and specific -- in their attacks on Sanders and socialism. Former Colorado Gov. John Hickenlooper summed up the argument during his speech at the Iowa Democrats Hall of Fame celebration in Cedar Rapids this weekend.

"We must present a bold vision for the future, but we also must acknowledge that the most effective attack the Republicans can level against us is 'socialism,' " Hickenlooper said. "Now, that does not mean that Democrats should shy away from big progressive goals. Far from it. A pragmatist doesn't say no to big ideas, they figure out how to get them done."

Sanders in his own remarks at the same event insisted, without mentioning socialism or any other candidate, that anything less than a full bore rejection of the status quo would leave voters cold -- and potentially dim their excitement ahead of the next election.

"I understand that there are some well-intentioned Democrats and candidates who believe that the best way forward is a middle ground strategy that antagonizes no one, that stands out to nobody and that changes nothing," Sanders said. "In my view, that approach is not just bad public policy, but it is a failed political strategy that I feel could end up with the reelection of Donald Trump."