“I think what they know is that four months ago, when I entered this race, if you look at the polls, I was in 3 to 4 percent,” he said during a campaign stop in Altoona, Iowa, according to CNN

ADVERTISEMENT

“[The] vast majority of the American people didn’t know who Bernie Sanders was, they didn’t know what my ideas were, and in [the] last few months, we have amassed huge amounts of enthusiasm and huge amounts of energy,” Sanders said.

“So obviously, I think the secretary’s people are getting nervous about the energy and enthusiasm our campaign is bringing forth,” the Vermont lawmaker added.

Sanders has seen a steady uptick in popular support since launching his White House run in May.

Clinton, in contrast, has seen her backing among voters slowly erode amid an ongoing scandal over her personal email server while at the State Department.

Critics say her use of a personal storage device while serving at the agency prevented accountability and potentially exposed sensitive national intelligence.

The resulting scrutiny has raised red flags among voters, some of whom now wonder whether Clinton is trustworthy and transparent enough for the nation’s highest office.

Clinton remains the frontrunner for the Democratic presidential nomination in 2016 despite the controversy.