Biden is expected to win big next week in primaries in Florida and Arizona,states where voters tend to be older and more conservative.

When Biden spoke to supporters in Pennsylvania,it was clear he was already thinking ahead to the general election in November.

Rather than delivering a triumphant victory speech,he praised Sanders and his supporters for their"tireless energy and their passion"and said there was a place for them in the party.

"We share a common goal,and together we'll defeat Donald Trump,"Biden said."We'll defeat him together. We'll bring this nation together."

Unusually,Sanders did not make any public appearances after the results came in.

Sanders backer Alexandria Ocasio-Cortez,the progressive congresswoman from New York,urged young voters to leverage their power to demand bold policies.

"Now is the time to ask for accountability,"she said on an Instagram video."And now is the time to ask for commitments - real commitments - not just gestures."

Both Biden and Sanders cancelled planned rallies in Ohio because of fears about the coronavirus,the first time this has happened during the campaign. A planned debate between Sanders and Biden in Arizona this weekend will be filmed without a studio audience.

Guy Cecil,the head of the Democratic Super PAC Priorities USA,tweeted:"The math is now clear. Joe Biden is going to be the Democratic nominee for president and@prioritiesUSA is going to do everything we can to help him defeat Donald Trump in November."

Former Democratic candidate Andrew Yang endorsed Biden on CNN,saying:"The math says Joe is our prohibitive nominee. We need to bring the party together. We need to start working on defeating Donald Trump in the fall."