Let there be no mistake: Obama, D-Ill., spoke extremely well and hit all the key notes he had in his 43-minute address before nearly 80,000 people. And after all the worries about echoes of Nuremberg rallies or ugly cult-of-personality hysteria, the atmosphere at Invesco was admirable -- much more a good-natured college football crowd for a key game late in the year than anything reminiscent of Big Brother.

Obama spoke with clarity and passion and delivered himself, as he had to, as a mainstream American with commonsense, decent and realistic answers to the problems of the American people. He should get a decent boost or "bounce" in the polls. In fact, Gallup reported Thursday that at long last after the first two ultra-liberal days of the convention, Obama was finally starting to get the boost he desperately needed, regaining a 5 percent lead over Republican presumptive presidential candidate Sen. John McCain, R-Ariz., by 48 percent to 43 percent.

While Obama's speech was very good indeed, it wasn't stellar -- and that difference matters. Earlier in the evening, former Vice President Al Gore delivered a far more effective speech than he ever did during his own star-crossed 2000 presidential campaign.

American national party conventions are always set up to crown a candidate who already has been clearly elected through the exhausting primary-caucus marathon. And all except the most inept losers, like Democratic President Jimmy Carter in 1980 or Republican nominee Sen. Bob Dole, R-Kan., in 1996, manage to look good before their home crowd audience.

However, the Democrats, in particular, have fielded an almost endless list of candidates over the past 20 years who spoke with power, sincerity, clarity and effectiveness to the American people on the last night of their conventions and came away buoyed by double-digit leads, only to see those leads evaporate like an ice cream cone in Death Valley at the height of summer as soon the Republican counterattack came on line.

Further, for all the predictable initial wave of wild enthusiasm for Obama's specificity in his speech, there really wasn't any new policy detail in it that did anything to reduce, let alone eliminate, the huge doubts over the credibility of his energy, fiscal, social spending and foreign policies.

Obama gave no hint how he was going to pay for his social policies. He gave no hint of any realistic policies to narrow America's out-of-control annual trade deficit or return the annual federal budget to the surplus levels it enjoyed under President Bill Clinton eight years ago. He offered not the slightest reassurance to the worries that foreign leaders, from Vladimir Putin in Russia and Hu Jintao in China to Iran's Mahmoud Ahmadinejad, and al-Qaida would take him for an easy mark and seek to bully or intimidate him as soon as he took office.

Obama's acceptance speech was deliberately timed to be on the anniversary of the great Dr. Martin Luther King's "I have a dream" speech in Washington 45 years ago, but that reminder proved a two-edged sword for Obama. He spoke extremely well, but like all his other speeches, this one didn't belong remotely in the same class with Dr. King's masterpieces. Yet his nomination was, of course, a celebration of how far the American people have come to fulfill Dr. King's great vision.

But in practical political terms, Obama didn't offer a hint of how he was going to pay for all the new programs he proposed while cutting taxes for 95 percent of working families.

Was his speech, then, just smoke and mirrors? Or did the master of the English language fail at third-grade arithmetic? Or did he just imagine that all the contradictions in his speech and his policies could be fudged away? That, after all, seemed to be the message of Obama's "can't we all get along" argument on social issues such as abortion, gay marriage and gun ownership.

Pro-choice and gay activists -- both groups that tended toward Sen. Hillary Clinton, D-N.Y., anyway, were certainly not going to like those parts of Obama's address. When he argued that it would be possible to provide the right for gay partners to visit in hospital and other situations without implementing same-sex marriage, did that mean he would oppose same-sex marriage as unnecessary to meet the practical concerns of gay partners?

Obama should have nailed down his post-convention bounce and restored his poll lead over McCain for the moment with his speech, but no more than that. The presidency of the United States is still in play.