Ask Sen. Barack Obama’s boss what the Illinois Democrat must do tonight before a cheering crowd of thousands to ensure residency at the White House next January, and Senate Majority Leader Harry Reid (Nev.) is loath to give his younger colleague any advice.

“One thing Barack Obama is blessed with is the ability to communicate,” Reid said in an interview this week at the Democratic National Convention in Denver. “He does a terrific job encouraging the American people. If he’s talking one-on-one with you, or if he’s talking to a crowd, it’s the same. He has the ability to instill hope.”

Obama will go before a prime-time national audience and 75,000 onlookers at Invesco Field at Mile High to accept his party’s nomination for president. The first-term Senator will try to widen his narrow lead in the polls by delivering a highly anticipated speech that not only showcases his skills as a masterful orator but also defies critics who say he’s too soft on substance.

Although Reid is keenly aware of Obama’s perceived shortcomings, he said he’s walking into tonight’s event confident that the junior Senator from Illinois — a once-in-a-generation politician, according to Reid — will exceed the expectations. Obama, Reid said, will inspire the masses tonight to support his historic candidacy, and also make plain that the Republican presidential contender, Sen. John McCain (Ariz.), offers no break from the last eight years of GOP White House control.

“Substance? John McCain is an empty suit,” charged Reid, who has served with Obama for just four years. “He’s not a maverick. He’s a clone of George Bush. Talk about substance. There’s no comparison between the two.”

For months, Democrats have tried to paint McCain as an adjunct of Bush, who in the waning months of his tenure continues to be highly unpopular, polls show. But McCain seems to be having some success convincing swing voters that he is independent of the current administration and in recent weeks has cut into Obama’s lead.

Majority Whip Dick Durbin (D-Ill.) — Obama’s closest Senate ally, who will introduce his home-state colleague at Invesco tonight — said he thinks Obama has lost some ground in recent weeks in part because of an advertising blitz by McCain, who has attacked Obama as a celebrity candidate who lacks the résumé to serve as president.

Durbin said he will try to reverse McCain’s newfound traction tonight, using his platform to “remind people where we were four years ago” and to set the tone for Obama’s speech, which he believes will be a healthy mix of the Illinois Democrat’s life story, goals for the country and outline for how his administration would differ from McCain’s.

“He’s going to make it clear that there’s a choice in this election,” Durbin said. “He obviously has to tell his story in a way that connects with people and let them know the distorted statements about him are not true. And secondly, while I don’t think he’ll be extremely specific on the issues, he will make the distinctions between himself and John McCain very clear.”

Some Democratic strategists have expressed concern that Obama threatens to reinforce the McCain camp’s attacks by staging his acceptance speech in a venue fit for a rock star. Given that danger, pundits have spent the days leading up to the convention counseling that Obama balance the visuals of swooning crowds with a speech that offers detailed policy prescriptions instead of the soaring but vague rhetoric he has become known for.

Obama this week indicated he would take that approach. “I’m not aiming for a lot of high rhetoric,” he said in an interview with USA Today. “I’m much more concerned with communicating how I intend to help middle-class families live their lives. I want people to come away saying, ‘Whether I’m voting for the guy or against the guy, I know what he stands for. I know what he believes.’”

But several of his Democratic colleagues on Capitol Hill said Obama should leave the white papers at home tonight. “I don’t think this is a wonkish night,” said Rep. John Larson (Conn.), vice chairman of the House Democratic Caucus. Added Rep. Artur Davis (D-Ala.), “I don’t think there’s going to be voters wanting to hear a 10-point plan from anybody. What they want to hear is that you have a sense of urgency about saving their lives. … I don’t think you should underrate the power of inspiration.”

Congressional Democrats say they have no doubt Obama will leave Denver tonight with the traditional post-convention bump that typically kicks off the final stretch of a general election campaign. The challenge for Democrats, however, will be to carry that boost forward beyond next week when the GOP convenes in Minneapolis/St. Paul to formally nominate McCain as its presidential nominee.

Sen. Byron Dorgan (D-N.D.) said that with 75 percent of the public unhappy with the direction of the country, Obama can do nothing but help his candidacy in a speech laced with promises of hope and new ideas. Dorgan said if Obama follows what’s been a successful playbook over the last 19 months of the campaign, he will “talk about the change he wants for our country’s future and talk to the American people about what kind of change that would be.”

Asked whether he was worried about whether Obama can carry the day with just more than two months to go until Election Day, Dorgan said: “Would I be more comfortable with a 20-point lead? Sure, but we’ve had a 20-point lead before and still haven’t been successful.”