Video

Senator Bernie Sanders of Vermont aggressively confronted voter concerns about his electability as president on Thursday, making a rare formal address to explain his left-wing ideology of democratic socialism and argue that its principles reflected mainstream American values like fairness and equality.

Mr. Sanders, who is hugely popular with liberals but is struggling to attract more voters to his Democratic presidential bid against Hillary Rodham Clinton, made blunt overtures to the party faithful by presenting himself as the heir to the policies and ideals of Franklin Delano Roosevelt and the Rev. Dr. Martin Luther King Jr.

Invoking the two men several times, Mr. Sanders said that democratic socialism was reflected in Roosevelt’s priorities like Social Security and in Dr. King’s call for social and economic justice, contrasting them to “socialist-communist” caricatures of his thinking put forward by Republicans to tar the Democratic field.

“I don’t believe government should take over the grocery store down the street or own the means of production,” Mr. Sanders said in an hourlong speech before a friendly audience of college students at Georgetown University in Washington. “But I do believe that the middle class and the working families of this country, who produce the wealth of this country, deserve a decent standard of living and that their incomes should go up, not down.”

Tapping into Democratic anger over income inequality and the power of big banks, Mr. Sanders also argued that the government bailouts of Wall Street firms during the Great Recession — and the lack of any prosecutions of industry executives — were a form of state-driven socialism in which a central government propped up and protected the wealthy.

Poor and middle-class Americans, by contrast, struggle financially without meaningful government help and end up being arrested on minor drug offenses, Mr. Sanders said, denouncing such fates by quoting Dr. King: “This country has socialism for the rich, and rugged individualism for the poor.”

“Wall Street C.E.O.s who help destroy the economy, they don’t get police records, they get raises in their salaries,” Mr. Sanders said. “It’s time we had democratic socialism for working families, not just Wall Street, billionaires and large corporations. It means that we should not be providing welfare for corporations. It means we should not be providing huge tax breaks for the wealthiest people in this country, or trade policies which boost corporate profits that result in workers’ losing their jobs.”

Mr. Sanders, who is running second to Mrs. Clinton in many national and state opinion polls but appears tied with her in the influential New Hampshire primary, has tried to portray his rival as a close ally of Wall Street who cannot be trusted to restructure the American economy to benefit the middle class. Many Democrats like the message more than the messenger, fearful that Republicans will tag him as a wild-eyed socialist — given his ideology and his calls for a “political evolution” — and crush him in the 2016 general election if he is the Democratic nominee.

Aware of this resistance from some voters, Mr. Sanders promised weeks ago to deliver a speech on democratic socialism, and it became one of the most anticipated of the presidential campaign so far. Mr. Sanders, who usually delivers his long speeches off the cuff, used a teleprompter to make his remarks, and campaign advisers in Iowa and New Hampshire were eager to see if the speech would persuade voters to give his candidacy a closer look.

“The clearer that Bernie is about democratic socialism, the more we’ll be able to pull in voters who may have misunderstandings about what the term is,” said Pete D’Alessandro, who oversees Mr. Sanders’s campaign in Iowa, which holds the first nomination contest on Feb. 1. Mr. Sanders hopes that underdog victories in Iowa and New Hampshire will give him enormous momentum against Mrs. Clinton.

In tackling a political vulnerability head-on, Mr. Sanders drew comparisons to some past presidential candidates who made speeches in critical moments, like Barack Obama’s remarks on race relations in 2008 — after inflammatory remarks by the Rev. Jeremiah Wright, then his pastor — and Mitt Romney’s speech on Mormonism in 2007 and John F. Kennedy’s speech on Roman Catholicism in 1960.

David Axelrod, who was Mr. Obama’s senior strategist during the 2008 race, said Mr. Sanders’s challenge was different from Mr. Obama’s, however.

“It was a crisis moment in our campaign, and it was difficult because he needed to strongly separate himself from his pastor’s statements without separating himself from the pastor,” Mr. Axelrod said. (Mr. Obama broke ties with Mr. Wright a couple of months later.) “Bernie’s candidacy isn’t in crisis because suddenly everyone thinks he’s a socialist. The issue here is, is that word a barrier for a sufficient number of voters that it creates an electoral ceiling for him? And can he persuade people that, if he were the Democratic nominee, ‘democratic socialism’ would not be a disaster in the general election?”

Seeking to puncture assumptions and fears about socialism, Mr. Sanders rejected the high taxation of some nations with democratic socialist welfare states, like Denmark and Sweden, and said he believed that more Americans could pay lower taxes — as long as taxes rose significantly on wealthy Americans and Wall Street firms.

He ruled out a socialist-style command economy and government-owned industries. But he said he wanted an America where people could work 40 hours a week and not live in poverty, and that such a society would require new government entitlements like free public colleges, Medicare-for-all health insurance, a $15 minimum wage, $1 trillion in public works projects to create jobs, and mandatory parental leave.

He also made blunt appeals to black and Hispanic voters, who are supporting Mrs. Clinton in far greater numbers, according to polls.

“I don’t believe in special treatment for the top 1 percent, but I do believe in equal treatment for African-Americans, who are right to proclaim the moral principle that black lives matter,” Mr. Sanders said, drawing huge applause for his use of a popular phrase for liberals and others denouncing police violence and social indifference to the needs of black people. “I despise appeals to nativism and prejudice, a lot of which we’ve been hearing in recent months, and I do proudly believe in immigration reform that gives Hispanics and others a pathway to citizenship and a better life.”

On foreign policy, Mr. Sanders emphasized that while he opposed war, democratic socialism did not rule it out, and that he would go to all lengths to protect Americans from terrorists and enemy nations.

“I am not a pacifist,” Mr. Sanders said twice during a question-and-answer session after the speech, noting that he supported the American-led invasion of Afghanistan and President Bill Clinton’s military strategy to end ethnic cleansing in the Balkans.

“I think war should be the last resort, but we have the strongest military on earth, and we should be prepared to use it when necessary,” Mr. Sanders said.

Unilateral military action would also be a final option in dealing with national security threats, he added, and he assailed the strategy of regime change for making matters worse over the decades in countries like Iraq, Iran and Chile. He said that he supported a “diplomatic plan” for President Bashar al-Assad to leave power in Syria, and that the destruction of the Islamic State inside Syria and Iraq remained “the highest priority.”

Douglas Brinkley, a historian at Rice University and the author of a coming book about Roosevelt, said the most powerful part of Mr. Sanders’s speech was wrapping himself in the mantle of the former president, though he could not predict whether it would ultimately be effective against Mrs. Clinton.

“Sanders is reminding people that he’s part of not only an important political tradition in American history, but a winning one,” Mr. Brinkley said. “Remember, F.D.R. won four times as essentially a democratic socialist.”