“I’m looking forward to laying out what’s at stake in this election,” Obama said in an afternoon conference call to supporters.

After a rousing warm-up act from former President Bill Clinton on Wednesday, delegates were keen to see some spirit from Obama himself.

“His job is about passion,” said Minnesota delegate Roxanne Mindeman. “He’s preaching to the choir, but he needs the choir to be motivated.”

The president, for his part, insisted there was no excitement deficit for his re-election bid, even if it lacks some of the verve that surrounded his historic election campaign in 2008.

“There’s plenty of enthusiasm out there,” he said. “The issue in this election is not going to be enthusiasm.”

In the lead-up to Obama’s big speech, senior adviser David Plouffe cautioned that no one should expect the president to slingshot out of the convention with a huge boost in polls that have long signaled a close race.

“You’re not going to see big bounces in this election,” said Plouffe, previewing the president’s speech on morning talk shows. He added: “For the next 61 days, it’s going to remain tight as a tick.”

GOP nominee Mitt Romney said he didn’t plan to watch the president’s address, but he weighed in from New England with some free speechmaking advice.

“What I’d like him to do is report on his promises, but there are forgotten promises and forgotten people,” Romney said. “Over the last four years, the president has said he was going to create jobs for the American people and that hasn’t happened.”

Citing a chance of thunderstorms, convention organizers scrapped plans for Obama to speak to an enormous crowd in a 74,000-seat outdoor stadium and decided to shoehorn the event into the convention arena, which accommodates 15,000. By late afternoon, a thunderstorm had popped up over the convention site, and the National Weather Service had issued a lightning advisory for the Charlotte airport.

That means no reprise of the massive show of support, excitement — and on-scene voter registration — from Obama’s 2008 acceptance speech before 84,000 in Denver. Republicans said Democrats made the switch because they feared the sight of empty seats.

Obama spoke to some of those bumped from the guest list during the afternoon call and said campaign officials would try to get them into other campaign events before Election Day.

“I know it’s disappointing,” the president said. But he asked supporters not to let their energy flag.

“This is still going to be a really close election, and the other side is preparing to release just a barrage of negative ads,” he said. “They are getting massive checks from wealthy donors. The good thing is, I’ve got you. So I really need your help, guys.”

In an election in which the economy is the top issue for voters, the president got some encouraging news from new reports that the number of people seeking unemployment benefits fell by 12,000 last week and that businesses stepped up hiring last month. Next up: The August jobless report, due Friday morning.

Even as the president asks voters to stick with him, Romney and the Republicans keep nudging Obama’s supporters to rethink their allegiance to a president seeking re-election in a time of weak economic growth.

The GOP nominee dropped in on a phone bank operation in Concord, N.H., where veterans in a campaign bus were calling other veterans to urge them to vote for Romney.

“We’re going to make sure that veterans have jobs when they come home from Afghanistan,” Romney said. The GOP nominee had been preparing for the fall debates at a private home in Vermont but headed back to his vacation home in New Hampshire on Thursday afternoon.

His party released a new ad Thursday, called “The Breakup,” in which a woman tells the president: “This just isn’t working … You’re not the person I thought you were. … I think we should just be friends.”

Anticipating a strong speech from the president, Republicans diminished the importance of Obama’s performance in advance.

“Great speeches do not make great policy,” Rep. Mario Diaz-Balart, R-Fla., said at an event organized by the Republicans in Charlotte.

Among those giving warm-up speeches for the president Thursday night: Vice President Joe Biden and actress Eva Longoria.

Longoria, appearing on NBC’s “Today,” said she’s “been in the trenches” for Obama defending his record and promised her speech will be very different from Clint Eastwood’s meandering remarks to the Republicans a week earlier.

“No empty chairs,” she promised, referring to Eastwood’s conversation with an empty chair representing Obama.

Others adding to the celebrity quotient in Thursday’s convention lineup were performers James Taylor, Marc Anthony, Mary J. Blige and the Foo Fighters. Actresses Scarlett Johansson and Kerry Washington both had speaking slots.

Sen. Dick Durbin, D-Ill., was speaking too, and he gave voice to the Democrats’ nervousness about the GOP advantage in fundraising during a morning interview on CNN, citing the dollars pouring in from Republican-leaning super PACs.

“We’ve got 17 angry, old, white men who are pouring in millions of dollars, carpet bombing every candidate in sight,” Durbin said.

First lady Michelle Obama aimed to help the Democrats catch up, appearing at a private meeting of Obama’s national finance committee. And Clinton popped out his second fundraising email in as many days.

The former president planned to campaign for Obama in Florida next week and was expected to make later appearances in the battlegrounds of Ohio, Pennsylvania and Virginia, according to a campaign official.

Underscoring the importance of a turn of phrase, the president said in a TV interview that he had “regrets for my syntax” when he told a campaign crowd last month that people who had a business “didn’t build that.” Romney turned the president’s line into a rallying cry, claiming Obama overstated the importance of government’s role.

But Obama said he stands by his point that the government has provided strong support to small businesses. “Everyone who was there watching knows exactly what I was saying,” he said in the interview with WWBT in Norfolk, Va.

GOP running mate Paul Ryan, campaigning in Colorado, needled Obama about the phrase anew on Thursday, saying government shouldn’t get the credit for business owners’ achievements. He lamented “the most partisan president, the most acrimonious climate, the bitter partisan environment.”

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Woodward reported from Washington. Associated Press writers Ben Feller, Ken Thomas, Matt Michaels, Jim Kuhnhenn and Leo Buckle in Charlotte; Jennifer Agiesta, Jack Gillum and Josh Lederman in Washington; Kasie Hunt in New Hampshire and Thomas Beaumont and Steve Peoples in Colorado contributed to this report.