The president, he said, “believes in corporate socialism for the rich and powerful. I believe in a democreatic socialism that works for the working families of this country.”
Speaking with the use of a teleprompter, Mr. Sanders delivered his speech in a small theater at the George Washington University, a dozen flags behind him. The venue, within walking distance of the bureaus of most major news organizations, was filled with people invited by the campaign, as well as members of the news media, which made up about a third of the audience.
His address appeared similar to one he delivered in November 2015 at Georgetown University during his first presidential bid. In that speech, Mr. Sanders — who at the time was mounting an underdog but surprisingly robust challenge to Hillary Clinton — also presented himself as an heir to the policies and ideals of Mr. Roosevelt and Dr. King and cast democratic socialism as a system that ensures people can have health care, access to higher education and jobs that pay at least a minimum wage.
In the political realm, socialism has become an elastic term that takes on different meanings depending on a person’s viewpoint and ideology. Mr. Sanders has taken pains to draw a contrast between his brand of democratic socialism and the kind that prescribes a command economy and government-owned industry. But at times in his long career in public service, he has also advocated for some policies that leaned toward a more traditional definition of socialism.
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In the 1970s, for example, he argued for nationalizing some industries, including energy companies and banks. And as mayor of Burlington in the 1980s, he went further than many Democrats in supporting socialist leaders. Throughout his political career, he has spoken of revolution, espousing a sympathy for the working class and the poor, whom he argues are suffering at the hands of profit-seeking corporations and the rich and powerful who lead them. One of his political heroes is Eugene V. Debs, the labor organizer.
While he remains popular with many in the progressive left, Mr. Sanders has been working in recent months not only to expand his base but also to retain the voters who supported him in 2016. A recent poll from the Des Moines Register and CNN showed that Mr. Sanders had lost ground over the last three months among likely Iowa caucusgoers, even as Senator Elizabeth Warren and Mayor Pete Buttigieg of South Bend, Ind. have surged.
A poll by Monmouth University released on Wednesday, an hour before Mr. Sanders’s speech was set to begin, showed Ms. Warren had surpassed Mr. Sanders among Democratic voters in Nevada, a key early state, with 19 percent support to Mr. Sanders’s 13 percent.