Bernie Sanders continued his presidential primary hot streak and won the Democratic contest in Wisconsin, the sixth race the Vermont senator has won in the last seven.

While all the votes are still being counted, multiple sources projected Mr Sanders as the winner in Wisconsin. Polls ahead of the primary had shown him to be slightly ahead of Hillary Clinton.

"Momentum is starting this campaign 60 to 70 points behind Secretary Clinton," Mr Sanders said in his victory speech on Tuesday from Wyoming. "Momentum is in the last two or three weeks that national polls have us either one point up or one point down."

Mr Sanders continues to win primaries, but he also has been beating Ms Clinton in fundraising, gaining momentum that has some pundits asking if he will be able to catch his opponent in the coming months.

The Sanders campaign raised $44 million in March, compared to $29.5 million raised by Ms Clinton, the Washington Post reported. That was a new record for Mr Sanders, topping the $43.3 million raised in February.

“What this campaign is doing is bringing together millions of people contributing an average of just $27 each to take on a billionaire class which is so used to buying elections,” Mr Sanders said in a statement last week. “Working people standing together are going to propel this campaign to the Democratic nomination and then the White House.”

In pictures: US Elections 2016 Show all 15 1 /15 In pictures: US Elections 2016 In pictures: US Elections 2016 Democratic U.S. presidential candidate Bernie Sanders speaks to supporters after rival candidate Hillary Clinton was projected as the winner in the Nevada Democratic caucuses Reuters In pictures: US Elections 2016 Democratic presidential candidate Hillary Clinton takes photos with workers at her campaign office in Des Moines, Iowa AP In pictures: US Elections 2016 Republican presidential candidate Mike Huckabee, second from left, prays before lunch with supporters at Drake Diner in Des Moines, Iowa Reuters In pictures: US Elections 2016 Democratic presidential candidate and former Maryland Governor. Martin O'Malley, speaks during a campaign stop in Waterloo, Iowa AP In pictures: US Elections 2016 Democratic presidential candidate Bernie Sanders speaks, as his wife Jane O’Meara Sanders looks on, at a campaign event at Iowa State University Getty In pictures: US Elections 2016 Republican presidential candidate Marco Rubio speaks at St. Ambrose University in Davenport, Iowa Reuters In pictures: US Elections 2016 Republican presidential candidate Ben Carson speaks at a campaign event at Fireside Pub and Steak House in Manchester, Iowa. Getty In pictures: US Elections 2016 Republican presidential candidate Rick Santorum visiting supporters at a house party in West Des Moines, Iowa Reuters In pictures: US Elections 2016 Republican presidential candidate Donald Trump at a campaign event in Cedar Rapids, Iowa AP In pictures: US Elections 2016 Republican candidate Ted Cruz campaigns at Greene County Community Centre in Jefferson, Iowa AP In pictures: US Elections 2016 Senator Rand Paul speaks during a Caucus rally at his Des Moines headquarters in Iowa Getty In pictures: US Elections 2016 Republican candidate Jeb Bush speaks at a campaign event in Des Moines, Iowa AFP In pictures: US Elections 2016 Former Alaska Governor Sarah Palin introducing the arrival of Donald Trump during a campaign rally in Cedar Rapids, Iowa Reuters In pictures: US Elections 2016 A portrait of Democratic candidate Bernie Sanders at his campaign headquarters in Des Moines, Iowa Getty In pictures: US Elections 2016 Campaign badges on sale ahead of a Trump rally at the Ramada Waterloo Hotel and Convention Centre in Waterloo, Iowa Getty

But as the momentum builds for Mr Sanders and the pressure mounts for Ms Clinton, the Sanders campaign must start winning big if the Vermont senator is to catch up to the former secretary of state. CNN reported that if Mr Sanders were to win the 21 remaining presidential primaries on the calendar with 55 percent of the vote, he still wouldn't be able to match Ms Clinton for delegates.

"What momentum is about is my belief is that if we wake up the American people...there is nothing that we cannot accomplish," Mr Sanders said Tuesday night.

Ms Clinton has 1,271 delegates to 1,024 for Mr Sanders. It takes 2,383 delegates to win the Democratic presidential nomination and all Democratic contests award delegates proportionally, based on number of votes.

Still, with Wisconsin in the books, 50 per cent of Democratic delegates remain. If Mr Sanders can continue to win and start winning bigger, his campaign will increasingly consider the possibility that their candidate could go to the Democratic National Convention in July with a chance to grab the nomination.

“We’ve mapped out a path to victory in our campaign in terms of delegates — pledged delegates — and we don’t have to win everywhere, but we do have to win most of the states coming up,” the Sanders campaign manager Jeff Weaver told MSNBC on Tuesday. “So there’s no one state that’s a must-win, and as we look forward we’re going to be able to accumulate the delegates we need to get the pledged delegate lead by the end of this primary and caucus process.”