‘Part celebration and part anxiety’

Striving for unity and spoiling for a fight with Republicans, Democrats from across the country gathered Sunday on the front edge of the Rocky Mountains for a history-making convention tinged with concern over a presidential race grown closer than many expected.

The nervousness belies broad political trends favoring the party and Barack Obama, its nominee-to-be: an unpopular war, a sour economy and a Republican president at basement level in opinion polls. Despite those advantages -- and his prodigious fundraising -- Obama’s lead in national surveys has all but evaporated over the last month, renewing concerns about the senator’s relative inexperience and political durability.

“It’s going to be part celebration and part anxiety,” Donna Brazile, who ran Al Gore’s 2000 presidential campaign, said of the Democratic gathering that begins today.

By sharpening his message over the next four days -- narrowing the gap between his high-flown rhetoric and voters’ kitchen-table concerns -- and building his image beyond a celebrity stereotype, the Illinois senator hopes to make the election a choice between himself and GOP Sen. John McCain, not just a straight referendum on Obama. He also hopes to patch, once and for all, his differences with Sen. Hillary Rodham Clinton and her followers.

“It’s important for him and the convention as a whole to lay out the distinctions and comparisons between himself and McCain,” said Jim Jordan, a Democratic strategist. “He needs to show that he can take off the gloves.”

Whatever happens in November, history will be made this week in the thin night air of Denver.

Obama’s nomination and his 50-yard-line acceptance speech Thursday in the city’s football stadium will not only cap a remarkable political upset, but will also represent a milestone: It will be the first time an African American carries a major party’s standard into the fall presidential campaign.

More than 50,000 visitors -- delegates, political dignitaries, protesters, lobbyists and thousands of reporters dispatched to chronicle their movements -- continued to pour into this capital city Sunday, beneath a sunny blue sky. Police swarmed downtown, giving the blocks around the convention site a paramilitary feel, and the week’s first organized protest -- an antiwar march -- came off without a hitch.

Campaigning Sunday in Wisconsin, a November battleground, Obama continued to sharpen his rhetorical attack on McCain, focusing on economic issues and offering, strategists said, a taste of the days to come.

“My main goal at this convention and through my speech is to convey a sense of urgency that so many families are feeling across the country,” Obama told the Denver Post in an interview published Sunday. “And to present a clear choice between continuing the same economic policies . . . and a new approach.”

Obama also needs to show -- if polls are any indication -- that he is more than a political flash with a gift for oratory and a pleasing but vague message of change. “He needs to introduce himself to voters who know him by name, but not by substance,” said Peter Hart, a veteran Democratic pollster.

The coming days and weeks will present the sternest test of Obama’s brief but charmed national political career.

He faces a party still not altogether healed from a long and bruising primary season. Perhaps the biggest question this week is how his vanquished opponent, Sen. Clinton of New York, and her most die-hard backers -- including her husband, former President Bill Clinton -- will comport themselves.

Sen. Clinton is the featured speaker Tuesday night on a program devoted to a celebration of women in politics. Although she has repeatedly endorsed Obama, there is simmering resentment in both camps over their primary battle. With little other drama this week, Clinton’s every move will be examined for any sign of equivocation or insincerity. The former president will address delegates Wednesday night and face the same scrutiny.

“They have to validate Obama,” said Brazile, a Washington, D.C., delegate who was neutral in the primaries. “She has to get up and tell her supporters, ‘I trust Sen. Obama to carry out the agenda we put forth in the primaries.’ And Bill Clinton has to say, ‘I believe he will make a great commander in chief. I know he has what it takes.’ ”

Making mischief, the McCain campaign Sunday broadcast a TV spot, “Passed Over,” that featured some of Clinton’s primary season attacks on Obama and suggested they were the reason he chose Sen. Joe Biden of Delaware as his running mate. Clinton, through a spokeswoman, reiterated her support for Obama and Biden.

Though her name will be placed in nomination, Clinton -- in a further conciliatory move -- is expected to release her pledged delegates Wednesday and urge them to cast their votes for her former rival.

Obama will not arrive in Denver until Wednesday. He plans to wend his way here after a tour of battleground states. Biden is due to arrive today and address delegates Wednesday night.

But even in his absence, the production is entirely Obama’s: the nightly themes and roster of speakers, the soundstage (which resembles a pinball arcade) and a decision to move his acceptance speech from the midsized Pepsi Center to nearby Invesco Field, which seats more than 70,000.

There will be two audiences this week, reaching far beyond the approximately 4,400 convention delegates, who split nearly evenly in their allegiance to Obama and Clinton.

One audience is the political chattering class nervous that Obama’s lead in national in polls has dwindled and wondering whether the first-term senator has the mettle for a fierce fight against McCain. Whatever else divides them, Democrats seem united in a firm belief that this week’s speakers must aggressively go after the Republican nominee in a way Sen. John F. Kerry of Massachusetts, the 2004 Democratic nominee, did not.

“That was a serious and, I believe, fatal mistake,” said California Democratic Party Chairman Art Torres. “You can’t do that in this kind of political environment with a 24/7 news cycle, the Internet, YouTube. . . . There has to be an aggressive compare and contrast.”

Anita Dunn, a senior advisor to the Obama campaign, suggested that Democrats needn’t worry. “This campaign presents a very stark choice to the American people,” she said. “We’re going to make that very clear.”

The second, and perhaps more important audience, is the millions of Americans watching from home, or reading about the convention, who tell pollsters they only vaguely know Obama, or harbor doubts about his candidacy because of his exotic name, his race or his lack of an extensive Washington resume.

Obama indirectly spoke to some of those concerns Sunday in Wisconsin. “I think what you’ll conclude is, ‘He’s sort of like us,’ ” Obama told supporters, citing his middle-class upbringing and financial struggles before two best-selling autobiographies made him a wealthy man.

A perception has grown up in recent decades that conventions -- which are no longer the decision-making bodies they once were -- have become irrelevant. But political experts disagree. “It’s a unique opportunity for candidates to focus attention on themselves and their message for four nights . . . mostly unvarnished and unimpeded,” said Mark Mellman, a Democratic pollster.

Even people who don’t pay attention to politics begin to tune in around convention time, said Don Sipple, a veteran GOP ad man. “It’s almost like a gateway to the real show, the fall campaign,” Sipple said.

Indeed, two-thirds of undecided voters sampled in the latest ABC-Washington Post poll said the Democratic and Republican conventions would be important in helping them make up their minds for November.

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mark.barabak@latimes.com

Times staff writers Michael Finnegan, Peter Nicholas and Nicholas Riccardi contributed to this report.