US democratic party unlike the republicans have a concept, called Super Delegates, these are the people who doesn't need to abide by popular vote and can choose whomever they like. This year there are 717 delegates up for grab.
Mrs. Clinton has so far secured support of 455 super delegates, while Bernie Sanders have only 22. That still leaves 239 delegates, who are yet to back any candidate and that may not happen until the very end.
However, that is not the biggest challenge facing Bernie Sanders. It's the win and win Margin. Even if all super-delegates support one candidate, math says other can still win nomination riding on popular vote.
Simple analysis, of the delegate data so far clearly indicates the problem facing Bernie Sanders,
He is losing big but winning small.
There are 50 US states and so far 21 has gone to vote. Our analysis shows the following –
Mr. Sanders has won in 9 states, while Mrs. Clinton has won in 12. But that's not bad, considering still 29 states yet to vote.
However, it is not like winner takes all. Delegates are distributed proportionately based on the vote gained and Mr. Sanders is clearly not winning big.
Average win margin (in delegates) for Sanders is about 9, whereas it is almost 23 for Clinton.
Biggest win margin for Sanders has been 16 and that is in his home state Vermont, where he grabbed all. While Clinton won 73 more delegates in Texas.
So, if Mr. Sanders to become Democratic nominee, he needs to win and win big. To win democratic nominations, candidate needs to win 2383 delegates and there are still 2973 candidates there, up for grab.
One positive for Sanders is Southern states, due to African-American lobby, Clinton was largely expected to win.
Latest scorecard shows, Clinton has amassed 1221 candidates and Sanders 571 so far.
Next big date is March 15th, when 5 states, Florida, Illinois, Missouri, North Carolina and Ohio go to voting, with 691 candidates up for grab.