Vying for the Democratic presidential nomination, Sanders has called for the universal expansion of Medicare, a social assistance program that just turned 50.

Sanders first made the announcement on Wednesday night, in a live-streamed speech to 3500 meetings of campaign volunteers across the US. He repeated the call on Thursday, the 50th anniversary of Medicare, at a campaign rally on Capitol Hill organized by National Nurses United and attended by members of many other labor unions.

"The time has come also to say that we need to expand Medicare to cover every man, woman and child as a single-payer, national healthcare program," Sanders said.

He took aim at the remarks by a Republican contender for the presidential nomination, Florida governor Jeb Bush, who said that he wanted to "phase out" Medicare and called the system "actuarially unsound."

"As we celebrate the 50th anniversary of Medicare, it is important that we defend this enormously important program rather than talk about ending it," Sanders said in a statement. "Our goal as a nation should be to join the rest of the industrialized world and guarantee health care to all Americans, not end a highly-successful program which protects seniors and the disabled."