DENVER — As Republican operatives scampered out of the Mile High City toward their own conclave in the Twin Cities, work crews tore down the GOP banners that scathingly referred to the Democratic convention as a mile high and an inch deep.

But for all the charisma, confidence and soaring oratory that Barack Obama displayed in Denver in becoming the first black presidential nominee of a major political party, the somewhat snotty GOP slogan hit on exactly why Obama has a huge challenge ahead of him.

Former President Bill Clinton said with newfound sincerity that Obama is ready to be president in an economic slowdown and ready to be commander-in-chief in time of war. But it was uncertainty about that very issue — Obama's lack of experience — that Republicans stoked in Denver and will harp on until November.

For a while, Obama was double digits ahead of John McCain in the polls. The race has tightened. Some political analysts think this may be the closest election in years, even surpassing the nail-biter of 2000.

Political conventions may seem like mastodons, but they have their usefulness. And as speaker after speaker in Denver praised Obama in language that was boringly the same (the Obama cadre of speechwriters honed nearly all the hundreds of speeches at the convention to drive home the same themes), the delegates left for the long slog to Election Day, beginning to believe and ready to pour their hearts into trying to get the skinny man with the funny name elected president.

This contrasted with the anxiety they felt on arriving, carrying their weird hats and deely boppers, battery-powered sparkly necklaces, badges, pins and questions about whether they were nominating the right candidate to win back the White House after eight years in the wilderness.

GOP pollster Frank Luntz specializes in running focus groups, where he gathers likely voters who say they haven't made up their minds on a candidate, and asks them to react by turning a dial to words about each nominee. About the group he ran in Denver, he said, they are torn between a desire for change and a need for experience, stability and accountability. Asked to describe Obama in one word, some of the voters used words such as scary, unaffordable and inexperienced. They described McCain as dependable, strong, patriotic and experienced. They said they are looking for accountability, trust, someone who understands voters' concerns and someone who is honest and ethical. Charismatic barely rated.

But the voters assembled were mostly white and middle-aged. Obama is hoping to attract new voters from young people, Latinos, blacks and women. He exploited his rock-star status by giving his acceptance speech before 75,000 people outdoors in a football stadium.

But after eight years of George W. Bush, people are tired of glibness and arrogance. They yearn for workable solutions. If Obama does not spell out detailed proposals to the almost endless list of national problems, he will be a disappointment. And he will not be elected.

Obama has to convince Americans he will be responsible about getting out of Iraq and restoring America's image abroad. He must reassure the middle class and all working families that his policies will help the economy pick up. He must work to provide them with jobs and pensions and vow their children will get the right education for the 21st century. He must deliver health insurance for all.

He has to promise progress on global warming and the deteriorating infrastructure. He must pledge to work with Republicans in Congress to make progress on protecting the environment, providing energy independence, promoting technology and science.

He must balance civil liberties and fairness with protection against terrorism.

A presidential candidate has a nearly impossible job. He must be sincere but not promise what people know he can't deliver. He must inspire confidence. He must be likable but voters must be able to picture him in the Oval Office making tough decisions.

Voters, too, have a tough job choosing a leader. Here's betting a lot of them won't decide until November.

Scripps Howard columnist Ann McFeatters has covered the White House and national politics since 1986. E-mail her at [email protected].