(CNN) -- Vice President Joe Biden ended months of intense speculation about his political future on Wednesday by announcing he wouldn't seek the presidency, abandoning a dream he's harbored for decades and putting Hillary Clinton in a stronger position to capture the Democratic nomination.
With President Barack Obama at his side in the White House Rose Garden, Biden said the window for a presidential campaign "has closed."
The question of whether Biden, 72, would enter the race has consumed Democrats for months. His announcement follows a period of deep -- and public -- soul searching about whether to run for the White House while grappling with profound personal grief after his son, Beau, died this summer from brain cancer.
The prospect of a run seemed to decline further after Clinton's commanding performance at the first Democratic presidential debate on October 13. Her poised demeanor and deft handling of tough questions left many analysts convinced that Clinton effectively froze Biden out of the race.
His decision means that barring unexpected developments, Biden's long political career, which includes nearly 40 years in the Senate and two terms as vice president, will end along with the Obama administration on January 20, 2017.
The task of coming from behind in a campaign that his potential rivals Clinton and Bernie Sanders had already been waging for months seems to have been too steep for Biden.
Had he jumped into the race -- in a move that would have been seen as a direct challenge to Clinton -- Biden would have faced a huge deficit in grassroots organization and fundraising dollars.
He did not appear to have a genuine route to the nomination, trailing Clinton and Sanders in every national polls. Biden trailed Clinton by more than 20 points in a CNN/ORC poll released Monday. He stood at 18% compared to Clinton's 45% and Sanders' 29%.
Biden's decision will come as a relief to the Clinton campaign, as the former secretary of state seeks to stabilize her White House push after months on the defensive over the email storm about which she will testify before Congress on Thursday.
It means that the Democratic nomination now comes down to a straight fight between Clinton and Sanders, assuming low-polling candidates such as former Maryland Gov. Martin O'Malley do not catch fire.
And it spares Obama the awkward prospect of watching his vice president and former secretary of state battle to succeed him.
Biden arrived at his decision after a political career that spanned 40 years and was bookended by tragedy. Soon after he won his Delaware Senate seat in 1972, his wife and infant daughter died in a car crash. Then in May 2015, his son Beau, an Iraq war veteran and his family's hope to forge a political dynasty, died.
Though devastated by the loss, Biden's consideration of a White House campaign may have been motivated by his dying son's plea that he make a third run at the presidency.
He went through a highly public period of mourning and testing of the political waters, pouring out his heart on Stephen Colbert's late night show, and emotionally admitting at public events that he simply did not know if his family had the emotional endurance for a race.
Biden's previous two campaigns, in 1988 and 2008, barely caused a stir and foundered to a large extent because of his own indiscipline, a trait that earned him a reputation as gaffe-prone and which, allied with a garrulous temperament, led some to believe he was not of presidential caliber. Still, he was chosen for the No. 2 spot by Obama for his long experience in foreign policy and his deep knowledge of the Senate.
Biden's career will now be remembered largely for his vice presidency, in which he was in the room for all major decisions and was at Obama's side through dramas including the killing of Osama bin Laden and the passage of health care reform. He masterminded the implementation of the $800 billion stimulus plan which Democrats credit for staving off a second Great Depression and brokered a deal in 2012 to avert the so-called fiscal cliff.
In the Senate, Biden will be most remembered for his long stewardship of the Foreign Relations Committee and his fiery questioning of conservative Judge Robert Bork, a Reagan nominee for the Supreme Court who was never confirmed.
But his most lasting contribution may be the way Biden lived his life. Every time fate dealt him a blow -- including serious health issues when he had a brain aneurysm in 1988 -- he got back up, refusing to be beaten. And with a dash of Irish blarney and his love for political combat, he maintained relationships across the political aisle that now seem like a throwback to a long-gone age of civility.
His political approach is tactile, and personal, interwoven with parables of working-class life, hewn from his upbringing in the gritty Pennsylvania city of Scranton and of family life in his adoptive state of Delaware.
But after spending the better part of 40 years being talked about as a potential president, Biden will likely not be able to look back on his decision to forgo a final 2016 run, without a tinge of regret that he fell just short of the highest prize.