The Democrats have been hopeful that a “blue wave” of voters will come to the polls on election day in order to give the party overwhelming support to retake the House of Representatives, and potentially the Senate.
The Senator said: “I know a lot of people talk about this blue wave and all that stuff.
“I don’t believe it.”
Mr Sanders insisted that rather than there being a giant surge in left-wing support, the election will be determined by just a handful of votes.
He added that it will make the vote “very, very close”.
While he was sceptical about the possibility of a “blue wave”, Mr Sanders did say that if Democrats take back the House, then they would become an “entity able to stand up to Trump”.
Mr Sanders was in Iowa helping to campaign for Democratic candidates JD Scholten and Deidre DeJear when he issued his warning.
Some believe the former presidential candidate and self-described democratic socialist may make another run for the presidency against Trump in 2020.
For the Democrats to retake the House, in addition to maintaining their current 194 seats, they will need to win a minimum of 24 Republican seats.
Recent polls suggest the Democrats have an 86 percent chance of winning 40 new seats.
However, some political commentators are sceptical, as every major poll predicted Hillary Clinton would defeat Trump in the 2016 presidential election.
Despite Mr Sanders’ scepticism, he says that the Democrats “absolutely” have a chance of regaining support from rural voters.
Mr Scholten is currently running to take Republican Steve King’s seat in Iowa’s rural 4th Congressional district.
Mr Sanders said: “Look, what the Republican Party is today – and I know some people think I’m being very partisan, but I’m really not.
“This is a party that worked as hard as they could to give a trillion dollars in tax breaks to the top one percent and to incredibly profitable large corporations.”
If the Democrats retake the House, they will also be able to select the next Speaker of the House, the second person in the line of succession if the President is forced to step down.