However, Debbie Wasserman Schultz, the chair of the Democratic National Committee (DNC), had for long urged the US mainstream media not to count superdelegates in there reports.

"Combining them (pledged delegates earned in state-by-state race and superdelegates) at each phase of this contest is not an accurate picture of how this works," said Wasserman Schultz in an interview with MSNBC in February.

In the Democratic field this election cycle, the 714 superdelegates, unpledged Democratic Party leaders who are free to support any candidate, can make their final decision at the national convention in July. So far, an overwhelming majority had declared support to Clinton.

"The way the media is reporting this is incorrect," said Wasserman Schultz.

Though admitting that it was uphill battle, Sanders had repeatedly argued that he would be able to persuade some superdelegates to switch allegiance.

Apart from leading Sanders in the number of pledged delegates and superdelegates, Clinton also leads the race in the number of votes cast. However, Sanders' one advantage over Clinton is hard to ignore.

According to PolitiFact.com, a project dedicated to "fact-check" of statements of politicians and the federal government, Sanders fared better against Trump than Clinton did in all polls over the last six weeks.

On Sunday, a new poll released by CBS News also found that while Clinton leads Trump in a hypothetical matchup with 48 to 33 percent in California and 49 to 34 percent in New Jersey, Sanders leads Trump by larger margins of 23 and 18 percent in the two states respectively.