The key to this confidence? Delegate math.
A Democratic candidate needs 2,383 delegates, or representatives who will vote for them at the convention, to be eligible as the party's nominee. Although Clinton has only won four more states than Sanders, she leads him by more than 200 pledged delegates, 760 to 546.
"The important point of winning the nomination is that the delegates were by no means way split evenly," Clinton campaign manager Robby Mook said on a call with reporters, although he noted that he “obviously” wished the final results in Michigan had been different.
"By virtue of secretary Clinton's huge margin of victory in Mississippi versus Sen. Sanders' narrow margin in Michigan, we won many more delegates than Sen. Sanders last night,” Mook continued.
Mook only talked about pledged delegates, which are bound to a candidate through the convention and are generally allotted based on how many votes a candidate has received and how many delegates are in each state. According to data from ABC News, Clinton has received more than 4.9 million votes so far, while Sanders has received nearly 3.3 million.
Mook did not mention Clinton’s huge lead in super-delegates, an unelected delegate who is free to support any candidate at a party's convention. Sanders supporters have maintained that super-delegates prevent the people from having their voices heard, and they have started several petitions to tell the super-delegates to honor the will of the voters.
Mook said a pledged delegate lead of over 200 is wider than President Obama’s ever was during the contested primary in 2008.
According to an analysis by ABC News, Sanders would need to win all of the 34 remaining contests by 11.1 percent to win the nomination, and that is assuming that he acquires the remaining uncommitted super-delegates and has at least 50 super-delegates switch their allegiance from Clinton.
Despite the steep path for Sanders, the Clinton campaign downplayed expectations for March 15, when a total of 793 delegates will be up for grabs in five states. Mook cautioned that the demographics of Missouri, Illinois and Ohio are similar to Michigan, and that Sanders could prevail in those states as well.
But, he said, even if Sanders wins in those states, the campaign is still confident the night would rack up bigger delegate wins for Clinton due to the contests in North Carolina and Florida.
“We are confident that we are nearing the point where our delegate lead will effectively become insurmountable,” Mook said.
ABC News’ Ryan Struyk contributed to this report.