Democratic presidential candidate Bernie Sanders said Thursday that economic security is essential to Americans achieving true freedom, a central tenant in his political philosophy of "democratic socialism."

The Vermont senator said the idea has roots in the legacies of President Franklin D. Roosevelt and Dr. Martin Luther King Jr.

"Real freedom must include economic security. That was Roosevelt's vision 70 years ago. It is my vision today," Sanders said in a speech at Georgetown University. "It is a vision that we have not yet achieved and it is time that we did."

Sanders' comments came during a defining speech about his views as he seeks to challenge front-runner Hillary Rodham Clinton for the party's nomination. Clinton in recent days has offered a veiled critique of Sanders for his support of a single-payer health care system, which she says will require middle-class Americans to pay higher taxes.

Sanders said his proposal would save families significant amounts of money."

"Health care should be a right of all people, not a privilege. This is not a radical idea," he said.

Sanders said Roosevelt was responsible for much of the social safety net enjoyed by millions of Americans today, from Social Security, the federal minimum wage, unemployment insurance, the abolition of child labor, the 40 hour work week, collective bargaining and strong banking regulations.

He said at the time, "almost everything he proposed, almost every program, every idea he introduced was called `socialist."' But he said the federal government's role in providing economic security for Americans had become "the fabric of our nation and the foundation of the middle class."

Without mentioning Clinton by name, Sanders said his candidacy was based on creating a political revolution of supporters to demand a better deal for the middle class.

He added: "So the next time that you hear me attacked as a socialist -- like tomorrow -- remember this: I don't believe government should take over the grocery store down the street or own the means of production, 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."