Presidential 2020 candidate Bernie Sanders confronted critics of his leftwing politics in a formal speech on Wednesday that sought to explain and forcefully defend democratic socialism – the economic philosophy that has shaped his decades-long political career.

Sanders, speaking to a friendly audience at George Washington University in Washington DC, presented himself as the heir to a progressive tradition championed by Franklin Roosevelt and Martin Luther King Jr as he argued that a wholesale “political revolution” was the only antidote to the “tyranny of oligarchs, multinational corporations, Wall Street banks and billionaires”.

“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 in a defiant, 45-minute speech. “It is the path that I call democratic socialism.”

The speech comes at a critical moment for the senator’s campaign, two weeks before the first Democratic presidential debate and amid rising tensions over what direction to move the party. The challenge facing Sanders, who consistently runs second in national and state polls behind Joe Biden, is whether he can convince Democratic voters that his populist platform is not a barrier to the presidency and that he is the strongest candidate to take on Donald Trump.

To make that case, Sanders on Wednesday turned to history, comparing the current political moment to the post-Depression years, when nationalism, bigotry and xenophobia were on the rise around the world.

“We in the United States, thank God, made a different choice than Europe did in responding to the era’s social and economic crises,” he said. “We rejected the ideology of Mussolini and Hitler – we instead embraced the bold and visionary leadership of President Franklin Delano Roosevelt, then the leader of the progressive wing of the Democratic party.”

Like Roosevelt, Sanders presented himself as a progressive visionary who could mobilize the opposition to the twin economic and social forces that helped elect Trump in 2016.

“In the year 2019 the United States and the rest of the world face two very different political paths.” Sanders said. “On one hand, there is a growing movement towards oligarchy and authoritarianism in which a small number of incredibly wealthy and powerful billionaires own and control a significant part of the economy and exert enormous influence over the political life of our country.

“On the other hand, in opposition to oligarchy, there is a movement of working people and young people who, in ever increasing numbers, are fighting for justice.”

Many Democrats disagree with his diagnosis of the current state of affairs and fear Sanders’ leftwing politics will be used to tar the entire party and deliver the presidency to Trump for a second term. “Bernie ❤ socialism … and so do his 2020 comrades,” said the subject of an email sent by the Republican National Committee moments before Sanders appeared on stage.

“Democrats must say loudly and clearly that we are not socialists,” the presidential candidate John Hickenlooper will say in a speech rebutting Sanders on Thursday. “If we do not, we will end up re-electing the worst president in our country’s history.”

Sanders said he anticipated “massive attacks from those who attempt to use the word ‘socialism’ as a slur.” He added: “I have faced and overcome these attacks for decades. And I am not the only one.”

He recalled Roosevelt, quoting from a 1936 campaign speech: “Never before in all our history have these forces been so united against one candidate as they stand today. They are unanimous in their hate for me – and I welcome their hatred.”

At that remark, which Sanders delivered with a characteristic roar, the audience rose to its feet, whooping and applauding. When the room quieted, Sanders quipped: “I must say, it does sound a little contemporary doesn’t it?”

Sanders accused Trump and the Republican party of “hypocrisy” for their attacks on his ideology and quoted King’s observation that the US “has socialism for the rich, rugged individualism for the poor”.

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

Sanders gave a similar address on democratic socialism during his first presidential campaign four years ago but the landscape has shifted dramatically since then.

Unlike the Democratic primary in 2016, when Sanders was the sole progressive alternative to Hillary Clinton, he now faces competition from a sprawling field that includes candidates who, like the party’s base, are young, diverse and progressive.

In the wake of Sanders’ first presidential bid, perceptions of socialism have changed, especially among young voters. A Gallup poll from 2018 found that a majority of young Americans have a positive view of socialism and a recent Axios survey found that 55% of women between the ages of 18 and 54 say they would prefer to live in a “socialist” country.

And yet a Gallup poll released in May found that less than half of American voters say they would vote for a “qualified presidential candidate who is a socialist”.

During his remarks, Sanders lingered on the concept of freedom – asking rhetorically: “What does it actually mean to be free?”

He followed with a series of questions: “Are you truly free if you are unable to go to a doctor when you are sick, or face financial bankruptcy when you leave the hospital? Are you truly free if you cannot afford the prescription drug you need to stay alive?

“To me, the answer to those questions, in the wealthiest nation on earth, is no, you are not free.”