DENVER — Sen. Barack Obama (D-Ill.) officially secured the Democratic nomination Wednesday night, ending one of the longest primary fights in modern history and placing the first black nominee for president on a major-party ticket.

In a carefully choreographed show of unity, Sen. Hillary Rodham Clinton (D-N.Y.), who waged a long and often bitter fight to be the first female nominee, stepped in to cut short the roll call vote that she had sought. The delegates then elected Obama by acclamation.

The symbolism was staged to overwhelm the back story of the convention, the infighting between the party’s new face and the its leading family.

But despite the show, there are indications that the fractures in the party have not healed.

Polls show that sizable numbers of Clinton supporters are considering voting for Republican John McCain, while others may sit out the presidential race. Supporters are still angry that Clinton wasn’t selected for vice president, and the nominee’s handling of the convention rubbed salt in the wounds.

“I’m not going to vote for Obama. I’m not going to vote for McCain,” said Blanche Darley, a Clinton delegate from El Paso, Texas. “I’m just not going to vote in that race.”

Not even Clinton’s announcement that she had cast her ballot Wednesday morning for Obama, nor her ardent call to defeat McCain, swayed Darley.

But it did sway Elaine Harris, a pledged Clinton delegate from West Virginia.

“When she told us how she voted, I decided if it was good enough for her, it was good enough for me,” Harris said. “Once she said that, I was OK.”

Wednesday began with the word being given to state delegations that the voting was to begin in the morning. But the plan allowed delegates to change their votes right up to 4 p.m., after Clinton called her delegates together to release them.

Thousands of delegates and supporters poured into the Korbel ballroom of the Colorado Convention Center to hear Clinton formally release her delegates for the vote.

“Yes, we didn’t make it,” she told them, along with a bank of television cameras. “But boy, did we have a good time trying.”

Clinton spoke of the importance of electing Obama instead of McCain, but she didn’t press her supporters to change their vote. Instead, she told them they should “vote what’s in your heart.” But there were boos and shouts of “Nooo” when Clinton announced to her delegates she was releasing them.

Voting started on the floor not long after. States reported mixed totals, but it was clear many Clinton delegates had switched their vote. Kentucky overwhelmingly supported Clinton in the primary but reported a 36-24 vote for Obama to the floor.