Democratic presidential hopeful Bernie SandersBernard (Bernie) SandersDe Blasio headed to Iowa to speak at political fundraiser Yes, spills happen — but pipelines are still the safest way to move oil Why sexual harassment discussions include lawmakers talking about Bill Clinton’s past MORE on Sunday said the Iowa caucuses could mark the beginning of one of the biggest electoral upsets in U.S. history.

“Well, Jake, you know, when we started this campaign here in Iowa, we were 50 or 60 points behind Secretary Clinton,” Sanders told host Jake Tapper on CNN’s “State of the Union.”

“We have come a long, long way,” he added. “And the reason for that is, we have 15,000 volunteers who today are going to be knocking on doors. They're going to be making telephone calls. They're going to be urging people in very large numbers to come out and vote.”

“So, I'm feeling good, Jake. Our issues are out there. People are really enthusiastic. And if people come out to vote, I think you're going to look at one of the biggest political upsets in the modern history of our country.”

He said if enough people turn out to caucus, then “we have got a real shot to win this.”

Sanders is neck and neck with Democratic front-runner Hillary ClintonHillary Diane Rodham ClintonO’Malley tells Dems not to fear Trump FBI informant gathered years of evidence on Russian push for US nuclear fuel deals, including Uranium One, memos show Pelosi blasts California Republicans for supporting tax bill MORE.

A new Bloomberg/Des Moines Register poll released on Saturday has the Vermont senator trailing by just 3 points in the first-in-the-nation caucus, within the poll’s margin of error.