Vice President Joe Biden declared Wednesday he won’t run for president in 2016, ending a months-long flirtation with a third White House campaign and setting him on a glide path toward the end of his decades-long political career.

Biden’s decision bolsters Hillary Rodham Clinton’s standing as the front-runner by sparing her a challenge from the popular vice president. In an extraordinary appearance in the White House Rose Garden, Biden said he always knew that the window for a viable campaign might close before he could determine whether his family was emotionally prepared for another campaign so soon after the death of his son Beau from brain cancer in May. Biden said his family was prepared to back him, but that he nonetheless would not be a candidate.

“Unfortunately, I believe we’re out of time,” he said, flanked by President Barack Obama and Biden’s wife, Jill.

A Biden aide said the vice president made his decision Tuesday night. Encouraged by some who were seeking an alternative to Clinton, Biden had spent the past several months deeply engaged in discussions with his family and political advisers about entering the primary. Yet as the deliberations dragged on, Democrats began publicly questioning whether it was too late for him to run, a notion that hardened after Clinton’s strong performance in last week’s Democratic debate.

Notably, Biden did not endorse Clinton or any of the other Democratic candidates. Instead, he used the announcement to outline the path he said the party should take in the 2016 campaign, including a call for them to run on Obama’s record. In what could have been a campaign speech, Biden deplored the influence of unlimited contributions on politics, called for expanding access to college educations and called on Democrats to recognize that while Republicans may be the opposition, they are “not our enemy.”

“While I will not be a candidate, I will not be silent,” Biden said. Democrats responded with nearly universal praise for the vice president and support for his decision.

Clinton, who spoke to Biden shortly after his announcement, took to Twitter to call him “a good friend and a great man.”

“Today and always, inspired by his optimism and commitment to change the world for the better,” she said.

Republican contender Donald Trump praised Biden and took a poke at Clinton in a single tweet: “I think Joe Biden made correct decision for him & his family. Personally, I would rather run against Hillary because her record is so bad.”

Wednesday’s announcement was a letdown for Biden supporters who had pleaded with him to run, and in increasingly loud tones as his deliberations dragged on through the summer and into the fall. For months, the 72-year-old Democrat made front pages and appeared on cable news screens as pundits mused about his prospects and Clinton’s perceived vulnerability. A super political action committee, Draft Biden, was formed with the explicit goal of getting him into the race.

At the White House, aides and longtime Biden loyalists had prepared for a potential bid, putting together a campaign-in-waiting should he decide to jump in. Last week one of those aides, former Sen. Ted Kaufman, wrote an email to former Biden staffers laying out the potential rationale for a Biden run and promising a decision soon. Biden spoke personally to many supporters.

As speculation about his plans reached a fever pitch, he kept up an intense schedule of public appearances, seemingly testing his own stamina for an exhausting presidential campaign.

Read more at the Associated Press.