John Edwards, former candidate for the Democratic presidential nomination and champion of organised labour, on Wednesday night sought to rally his party and bring the primary race to a close by providing Barack Obama with his highest-profile endorsement in months.

Mr Edwards’ timing was also aimed at neutralising the fall-out from Hillary Clinton’s crushing victory in West Virginia on Tuesday night. White working class voters gave Mrs Clinton a 41 percentage-point victory over Mr Obama.

The move was the second piece of bad news for Mrs Clinton on Wednesday, after Naral, the women’s pro-choice group, switched its support to Mr Obama. Emily’s List, the group that campaigns for women to be more widely elected in Democratic positions, described the move as “enormously disrespectful”.

The announcements came as a slap in the face to Mrs Clinton, who was still touting her victory over Mr Obama in West Virginia. Before he dropped out, Mr Edwards was seen as the strongest blue-collar candidate in the race. His wife Elizabeth had earlier raised doubts about whether her husband would back Mr Obama after she attacked his healthcare plan and spoke favourably of Mrs Clinton.

In receiving his endorsement, Mr Obama will also be hoping to win over a majority of Mr Edwards’ 19 elected delegates, although Mr Edwards cannot instruct them which way to vote.

In the past week, Mr Obama has picked up the endorsement of almost 30 “superdelegates” – the unelected Democratic officials who will decide the nomination. Mrs Clinton has attracted two.

Mrs Clinton has vowed to continue her campaign at least until June 3, when the final two states – South Dakota and Montana – have their say.