While it is certain Obama will be nominated, it is unclear how smoothly the nomination process will go because Obama and and N.Y. Sen. Hillary Clinton's names are both being placed in nomination.
Obama's plane landed in Denver around 4 p.m. Chicago time.
Meanwhile, the delegations were still waiting to see how this nomination will play out, but it will be historic because when it's concluded, it will mean Obama has become the first African-American presidential nominee.
It typically goes by roll call vote by state, and that roll call vote was very important to Clinton supporters wanting to make sure to show off the amount of support she had. Others say perhaps they're going to let just Illinois or New York cast their votes.
Some of the speakers Wednesday will include Chicago's Mayor Richard Daley around 6 p.m. Later in the evening, former president Bill Clinton and vice presidential candidate Joe Biden will address the convention. The former president has been challenged to show support for Obama, the man who beat his wife to the nomination. During the campaign, he worked hard, at times drawing attention to himself.
"This whole thing is the biggest fairytale I've ever seen," Bill Clinton said at one point during primary campaigning.
Bill Clinton got angry over what he thought were unfair attacks against Hillary Clinton, and questions were raised about how prominent a role he should have in the campaign.
The other question on attendees' minds Wednesday was whether his speech could possibly overshadow that of Biden. His is the closing speech and it's believed he will play the attack dog role, striking out hard against Republican presidential candidate Ariz. Sen. John McCain. He will also tell part of his personal story, the tragic death of his wife and daughter in a car crash more than 30 years ago.
"It's a great honor to be nominated vice president of the United States, and I'm proud of it. And I don't mean in any way to diminish it, but it pales in comparison to the honor that I've had representing you," Biden said.
Obama is scheduled to speak Thursday night at Invesco Field to a crowd of nearly 75,000.
On Wednesday afternoon, Hillary Clinton held a meeting of her pledged delegates and told them that they are released from their responsibilities. They are not pledged to her anymore. They can vote for whomever they wish when it comes to the roll call vote. She did not tell them how to vote.As many in the room yelled, "No," Clinton said that, while she was releasing the delegates she had won in the primaries, "I am not telling you what to do. You've come here from so many different places having made this journey and feeling in your heart what is right for you to do."
Former Clinton advisor talks about Biden and roll call vote
David Wilhelm used to manage Bill Clinton's campaign. He made headlines earlier this year when he endorsed Obama and not Hillary Clinton. And he's one of many key Democrats calling for unity.
He not only managed Bill Clinton's campaign, he managed Mayor Daley's campaign as well as Biden's. Now he's a superdelegate from Ohio. And even Wilhelm said he had no idea how the roll call would work
"At the Ohio delegation this morning we were asked to sign a sheet of paper," he said. "It wasn't really a ballot… essentially our sign-in sheet, and we were asked who would we vote for last night. And even in Ohio, where most of the delegates are committed to Hillary Clinton it would appear that most people signed Barack Obama. But there was confusion in the morning, and I heard the state party chair say that the decision had not been made yet how this would proceed."
Wilhelm said he felt that Hillary Clinton's speech Tuesday night went a long way to providing the unity many hope will come out of the convention.
"And I think the speeches tonight will leave people with an unmistakable notion of the stakes involved in this general election and the contrast on economic policy and national security policy between Barack Obama and John McCain. So I think a lot of big work is getting done at this convention," Wilhelm said.
Wilhelm said the campaign will want the vice president to be the attack dog from time to time and to draw very clear contrasts between the two candidates.
"You do not want to have the principles that Barack Obama carries, the sharp-hard-edged message day after day," said Wilhelm. "So I think you will see some of that from Joe Biden. Joe Biden provides tremendous, tremendous credibility on national security and he has this authentic, middle class voice. So I think people are going to be very happy about what they see in Biden tonight."
Bill Clinton will say in a roughly eight-minute speech that only a Democrat in the White House can "restore America's standing to what it was eight years ago," said the aide, who spoke on the condition of anonymity because he was not authorized to pre-empt the former president's speech.
House Speaker Nancy Pelosi, presiding officer of the Democratic National Convention, predicted the roll-call voting after the names of both Obama and Clinton were put in nomination would go "very smoothly."
"Are you ready for victory? Then you must be ready for unity. That is the only way we are going to win and have this victory," she told Iowa's convention delegates.
Many details remained unknown, however, including how many states would vote before somebody -- probably Clinton herself -- asked the delegates to give the nomination to Obama by acclamation.
Clinton won 18 million votes in primary-season contests but failed to earn her party's nomination.
Pennsylvania Gov. Ed Rendell, who had been a Clinton supporter, suggested in an interview with The Associated Press that some delegates would vote for Clinton no matter what she said, and that any motion to move to an unanimous convention ballot would draw "a few no's."
On Friday, Obama, his wife Michelle and Biden and his wife Jill will embark on a three-day bus tour of battleground states Pennsylvania, Ohio and Michigan.
Representatives of the Clinton and Obama teams struck a deal setting ground rules for the roll call vote that will hand the nomination to Obama but will also allow Clinton supporters to express their support for her.
Advisers to Clinton and Obama sent a joint letter to state delegation chairs instructing them to distribute vote tally sheets to delegates Wednesday and return them before the vote got under way.
The letter, first obtained Tuesday night by The Associated Press, said Clinton would have one nominating speech and two seconding speeches, followed by Obama's nominating speech and three seconding speeches -- totaling no more than 15 minutes for each candidate. Then the roll call would begin, said the letter signed by Obama senior adviser Jeff Berman, Clinton senior adviser Craig Smith and convention secretary Alice Germond.
Kathleen Krehbiel, an Iowa delegate who had supported Clinton, credited the New York senator's convention speech Tuesday night for finally persuading her to cross the line and vote for Obama.
"My horse is out of the race. I'm getting out to work for Obama," Krehbiel said. But, she added, "I think there are a few delegates who need to vote for Hillary to reach that point of closure."
In a sign of unity, Obama adviser Berman and Clinton adviser Smith told delegates on Wednesday that they had been working out of the same office all week to ensure a smooth convention.
"The story is that we are working as a team," Berman said.
Anticipating Wednesday night's focus on national security at the convention, McCain contended in a new TV ad that Obama showed he was "dangerously unprepared" for the White House when he described Iran as a "tiny" nation that didn't pose a serious threat.
"Iran. Radical Islamic government. Known sponsors of terrorism. Developing nuclear capabilities to 'generate power' but threatening to eliminate Israel," says the ad, which was being run in key states. "Terrorism, destroying Israel -- those aren't 'serious threats"'?
Missing from the ad was the context of Obama's remarks last May in which he compared Iran and other adversarial governments to the superpower Soviet Union. "They don't pose a serious threat to us the way the Soviet Union posed a threat to us," he said in arguing for talks with Iran. "You know, Iran, they spend one-100th of what we spend on the military. If Iran ever tried to pose a serious threat to us, they wouldn't stand a chance."
The Associated Press contributed to this report.