Senator Bernie Sanders, second only to former Vice President Joseph R. Biden Jr. in the polls, is seeking to build on the momentum from his 2016 presidential run and shore up support among the left.

On the campaign trail, Mr. Sanders often reminds rallygoers that many positions popular among Democratic candidates today were viewed as unorthodox when he first ran on them in 2016. And as he looks to the general election, Mr. Sanders also frequently labels President Trump as a liar, racist and sexist while making the case that Mr. Trump has broken promises about protecting the social safety net and health care.

His political impact

What Mr. Sanders SAID

“Four years ago, when we said that health care is a human right, we were told that was a radical idea , that the American people wouldn’t accept it. Poll just came out the other day, consistent with other polls, 70 percent of the American people support a ‘Medicare for all’ single-payer program.”

— Asheville, N.C., in May

This is exaggerated.

While “Medicare for all” has grown more popular since Mr. Sanders campaigned on it in 2016, not all polls show as many as 70 percent of Americans supporting it.

As lawmakers began working on a health care overhaul in 2009, support for a single-payer system hovered from about 30 to 50 percent in most polls. When the Affordable Care Act became law a year later, national discussions of single-payer systems dissipated and sporadic polling showed that public opinion toward such systems did not change much from the end of 2009 to 2014.