The race for delegate-rich states such as New York, Wisconsin, Pennsylvania and California continues as Democratic candidates enter the second half of the primary season.
While it seems almost impossible that Mr Bernie Sanders could win New York - Mrs Hillary Clinton's home state - the senator from Vermont has a chance in Wisconsin and California, where his campaign is slowly gaining ground on the former secretary of state, according to polls.
Though chances of becoming the eventual party nominee are slim, he will likely stay in the race, experts say, not only because he has the funds to do so, but also to prove that a campaign funded by the American people can make it to the very end.
Building on his unexpected win in Michigan, followed by good showings in Alaska, Washington and Hawaii on March 26, the Sanders campaign is hoping to continue his winning streak in Wisconsin, which votes today.
The latest Marquette University Law School Poll showed Mr Sanders ahead of Mrs Clinton by 4 percentage points in the state. Four months ago, Mrs Clinton was ahead in that poll by 9 percentage points.
Political science professor Barry Burden, who is the director of the Elections Research Centre at the University of Wisconsin-Madison, said: "Sanders' strengths in Wisconsin are its large progressive white population, open primary and sizeable college student population. All three of those factors should help him be competitive in the state."
An open primary means that independents (and, by the same token, Republicans) can vote for Mr Sanders without registering as Democrats.
Michigan too held an open primary, where about three-quarters of independent voters opted for Mr Sanders, resulting in an unexpected win for him. The very same thing could happen in Wisconsin. There are 96 delegates at stake in Wisconsin, and a big win here would not only add to his delegate count, but also add momentum to his campaign.
At the moment, including superdelegates, Mrs Clinton has 1,712 delegates, while Mr Sanders has 1,011. The Democratic candidate needs 2,383 to clinch the party's nomination.
Mr Sanders has told supporters that although the bulk of the 712 superdelegates have declared support for Mrs Clinton, he is convinced they will come over to his side if he continues to do well in the primaries.
But experts are not convinced.
Professor Mack Shelley from Iowa State University said: "He may wind up winning a chunk of the 212 superdelegates who have not committed, but converting people would be much more difficult."
Looking beyond Wisconsin, winning important states such as Maryland and New York is also going to be tricky for Mr Sanders.
"There are significantly larger minority populations in New York and Maryland than in Wisconsin, and Clinton has done a better job of attracting minority voters," said Professor Irwin Morris, chair of the department of government and politics at the University of Maryland.
Mrs Clinton also has a huge lead of 27 percentage points in her home state.
"Things look fairly bleak for Sanders in New York, owing to the closed nature of the primary system in the state and the early deadlines for registering with a party," said assistant professor of political science Jacob Neiheisel from the University at Buffalo.
Despite expected losses ahead, experts say it is unlikely that Mr Sanders will bow out soon.
Prof Burden said: "Sanders says that he intends to win the nomination and would stay in the race even if he cannot win the nomination as a way to continue spreading his message."