US Vice President's announcement boosts Clinton's White House hopes

Following Joe Biden's announcement that he will not join the 2016 White House run, Hillary Clinton's prime challenger now is U.S. Senator Bernie Sanders of Vermont. 

Sanders is a self-styled democratic socialist, who has galvanized the party's left wing but has yet to prove he can broaden his appeal.

"It's an easier path for Hillary Clinton now," said Democratic strategist Bud Jackson. "Most polls reflect that without Biden in the race, it's more beneficial to her."

But Biden supporters did not appear to be falling in line behind Clinton after the announcement, with 15 of the 27 contacted by Reuters saying they were unsure they would back her.