Democratic presidential hopeful Bernie SandersBernie SandersParliamentarian deals setback to GOP repeal bill OPINION | Hey Dems, Russia won't define 2018, so why not fix your party's problems instead? OPINION | They told us to abandon ObamaCare — then came the resistance 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 Rodham ClintonTrump claims Trump Jr. 'openly gave his emails to the media' Trump: Mueller and Sessions should investigate Clinton ties to Russia OPINION | How Chris Christie went from America's straight shooter to Trump's crooked yes-man 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.