DENVER — Joe Biden got the call from Barack Obama while accompanying his wife as she was getting a root canal.

As he waited in the dentist office Thursday, Biden's cell phone rang with the presidential candidate's invitation to be his running mate.

It capped a six-week process of elimination that always pointed in Biden's direction even if the Delaware lawmaker couldn't believe he would actually be the pick.

The Democratic ticket, revealed Saturday in Springfield, Ill., began to form when Obama approached Biden in July and asked him if he'd consider being a contender for vice president, according to two Biden associates.

Biden said he would and submitted the requisite paperwork to the vetting committee but was skeptical that it would ever happen. A longtime friend who requested anonymity to speak freely said Biden wouldn't allow himself to believe he was in serious consideration because his hopes and expectations had been beaten down so much by such a miserable showing in the Democratic presidential race.

In the end, it came down to Biden, Indiana Sen. Evan Bayh and Virginia Gov. Tim Kaine, said several people involved in the deliberations. Kansas Gov. Kathleen Sebelius also was a strong contender but dropped out of contention as Obama focused on the other three.

Hillary Rodham Clinton, who ran so closely to Obama in the primary, was never seriously considered, said two officials involved with the search. She asked not to be vetted unless she was going to be picked, the two officials said, speaking on a condition of anonymity to describe the private discussions.

In the final days before the announcement, Obama's staff prepared for an announcement of Biden, Bayh or Kaine — and Obama had made his decision by Thursday and called them all that day to tell them their fate.

Obama campaign strategist David Axelrod described the search as "a long process, but it always pointed in Biden's direction."

Illinois Sen. Dick Durbin said he talked with Obama about potential candidates three weeks ago on a campaign bus swing through Florida. They made pro-and-con sheets and speculated about how the candidates would respond to various scenarios.

"Many others were discussed, but my impression was that those three a few weeks ago were really the centerpiece — Kaine, Bayh and Biden," Durbin said. He added that he didn't learn of the pick until Saturday morning, although he suspected which direction Obama was going.