Former secretary of state Hillary Clinton consolidated her position as the presumptive nominee for the Democratic Party after decisive wins in four of the five contested states on Tuesday, causing experts to question Senator Bernie Sanders' viability moving forward.
Mrs Clinton had strong wins in Florida and North Carolina, completing a clean sweep of all the south-eastern states, showing her popularity with black and minority voters.
She also topped Mr Sanders in Illinois and Ohio, an important swing state in the north-eastern part of the country, winning 56.5 per cent of the votes over Mr Sanders' 42.7 per cent. Missouri resulted in a virtual tie, with Mrs Clinton merely 0.2 percentage points ahead. A recount is likely, though victory will largely be for bragging rights, given that the state's delegates are allocated proportionally.
While her win was expected, the Sanders campaign was hoping for a surprise victory much like the one in Michigan last week, when he eked out a win even though all the polls favoured Mrs Clinton.
"The question was whether Sanders could gain from his surprise victory in Michigan last week, especially in states like Illinois and Ohio," said Dr Sara Moats from the Department of Politics and International Relations at Florida International University. "So it was a good night for Hillary."
Mr Sanders has not announced any plans to quit the race but would need extensive victories to overturn Mrs Clinton's lead.
"Sanders' chances of winning are not great," said Professor Jeffrey Hill, chair of the Department of Political Science in Northeastern Illinois University. "But he will stay in the race because he has already pushed Clinton to be more liberal than she would have been. By staying in, he keeps this pressure on her."
When we hear a candidate call for rounding up immigrants, banning all Muslims... that doesn't make him strong - it makes him wrong.
We cannot go forward unless we deal with the realities of American society today. And that is what we're going to do.
Over the campaign season, Mrs Clinton has moved to the left on issues such as free trade, and many have noted her tone on free college education has almost merged with Mr Sanders' in a bid to win over younger voters who support the Vermont senator.
"I think Sanders will stay in for at least another cycle but at some point he has to ask himself if he can still win the race and if he should continue to spend money," said Associate Professor Daniel Franklin, a political scientist at Georgia State University .
Even cable networks appeared to be putting Mr Sanders on the back burner, choosing to cover Mrs Clinton's victory speech in full on Tuesday night, while many completely ignored Mr Sanders' speech in Phoenix, Arizona, which will vote on March 22.
Although Mr Sanders emerged with no significant wins, his supporters in Phoenix seemed energised by his presence. "Phoenix, are you ready for a political revolution? Are you tired of a handful of billionaires running our economy? If you are, you have come to the right place," he said, prompting a deafening cheer from the young crowd.
In terms of the delegate race, there is no denying that Mrs Clinton is pulling ahead of Mr Sanders.
A Democratic candidate needs 2,383 delegates to win a nomination, and Mrs Clinton already has at least 1,561 after Tuesday's wins, nearly double Mr Sanders' 800.
Moving forward, Mrs Clinton is likely to focus more on the general election and beating the prospective Republican nominee, said experts.
During her victory speech in West Palm Beach, Mrs Clinton made many references to Republican front runner Donald Trump, saying: "Our commander-in-chief has to be able to defend out country, not embarrass it; engage our allies, not alienate them; defeat our adversaries, not embolden them."
But experts say she will also continue to address Mr Sanders in the hope of inheriting his supporters, whom she will need in order to win the general election.
"She has to be a little careful in her campaigning, balancing the need to beat Sanders in the primaries with the need to not alienate Sanders supporters," said Prof Hill.