US vice president Joe Biden rules out entering presidential race
US vice president Joe Biden has ruled out running for president in 2016.
His decision finalises the Democratic Party's field of White House candidates and sets Mr Biden on a path towards the end of his decades-long political career.
Mr Biden had spent months deliberating with his family and political advisers about a potential late entry to the Democratic primary.
But he also said he might not be emotionally ready to run after his 46-year-old son Beau died of brain cancer in May.
Mr Biden's decision bolsters Hillary Clinton's standing in the Democratic primary by sparing her a challenge from the popular vice president.
Mr Biden announced his decision in the Rose Garden, flanked by US President Barack Obama.
As Mr Biden's deliberations dragged on, Democrats began publicly questioning whether it was too late for him to run, speculation that intensified after Mrs Clinton's strong performance in last week's Democratic debate.
The announcement was a disappointment for Mr Biden's supporters who had pleaded with him to run.
For months, the 72-year-old Democrat made front pages and appeared on cable news screens as pundits mused about his prospects and Mrs Clinton's perceived vulnerability.
A super political action committee, Draft Biden, formed with the explicit goal of getting him into the race.
At the White House, aides and long-time Biden loyalists had prepared for his potential bid, putting together a campaign-in-waiting ready to move fast should he decide to enter the race.
Last week one of those aides, former Senator Ted Kaufman, wrote an email to former Biden staffers laying out the potential rationale for a Biden run and promising a decision soon.
Mr Biden and his team had lined up potential staff and enlisted donors willing to help; Mr Biden spoke personally to many supporters.
But Mr Biden broadcast his reluctance to run amid doubts that he and his family were emotionally ready in the wake of Beau Biden's death.
In a September appearance on The Late Show, Mr Biden told comedian Stephen Colbert he was still experiencing moments of uncontrollable grief that he deemed unacceptable for a presidential aspirant. "Sometimes it just overwhelms you," he said.
Both Mrs Clinton and Vermont independent Senator Bernie Sanders have been in the race since April - giving them a powerful head start in fundraising, volunteers, endorsements and voter outreach.
Democratic operatives and donors already committed to Mrs Clinton would likely have had to defect to Mr Biden in order for him to have viable shot at the nomination.
Mr Biden now approaches the end of his long career in politics.
A month after being elected to the Senate in 1972 aged 29, Mr Biden's wife and baby daughter died when their car was involved in a collision. Mr Biden considered giving up his seat, but instead was sworn in at the hospital where his sons, Beau and Hunter, were recovering.
Over six terms in the Senate, he rose in the ranks to become chairman of the Senate Judiciary and Foreign Relations committees, developing broad expertise in global affairs and a reputation for a plain speaking, unpredictable approach to politics.
Mr Biden twice ran for president. His most recent attempt in 2008 ended after he garnered less than 1% in the Iowa caucuses. His first run in 1987 ended even quicker, following allegations he plagiarised in some speeches.