Why does a star like Obama -- who can draw 200,000 Germans to the Brandenburg gate and 73,000 wildly enthusiastic supporters who will gather at Invesco Field for his acceptance speech Thursday night -- have a problem?
A state senator who served with Obama in the Illinois Legislature and supports him strongly confided one nagging concern many months ago.
"He and I agreed on a lot of bills, but I never saw him care so deeply about an issue that he was wiling to go down in flames for it," the legislator said.
It's the passion thing.
And so this U.S. senator from Chicago's South Side, despite his rocket ride to the nomination, still faces an uncertain landing.
If anything can gin up some raw emotion in the electorate, you would think that McCain's not knowing his many addresses might do the trick.
And Obama instantly seized upon it to say that most Americans don't live in McCain's rarified economic air.
But Obama is a guy, wide smile and well-crafted message notwithstanding, who seems to give the electorate more of his head than of his heart. And though, lord knows, after George Bush we need a president with a head, the heart part is not incidental.
In Colorado, he will face one of the big tests. It is one of a dozen battleground states where the presidency will be won or lost. Right now, polls here mirror the national picture: It's pretty much a dead heat.
There are far fewer people living in this entire state than live in the corridor from Chicago to Naperville to Joliet. The 2006 U.S. census puts Colorado's population at about 4.7 million compared to 7.9 million living between Lake Michigan and Will County.
The November election is a state-by-state proposition; it's about electoral votes, not simple majorities.
And Team Obama is aware of the difficulties. They've met them before in places like New Hampshire and Pennsylvania.
This week in Denver will be a showcase of all that the Obama campaign has brought to bear: incredible discipline, message control and a fund-raising machine unlike any other.
It will also bring the state of Illinois onto a national stage as others, most notably Michelle Obama, explain to a country that is finally focusing on November, who her husband is.
And the Illinois convention delegation, dysfunctional Democratic family though it may be, will put the full force of its Obama enthusiasm on display here in Denver.
Tammy Duckworth, the wounded veteran who now heads the state's Veterans Affairs department, will have a prominent role. State officeholders and likely gubernatorial candidates Lisa Madigan, Dan Hynes and Alexi Giannoulias will share their passion about what it means to represent Illinois, and what Illinois says about Obama.
Conventions, however tightly scripted, however lacking in surprise, are gathering points -- places to put some gas in the party's tank for the trip to November.
Illinois will be a star here with a front-row seat thanks to Dick Durbin, our senior U.S. senator, who early and often argued that Obama's time has come.
All that emotion, all that heart, will be on Illinois' sleeve this week in Denver. And Obama's challenge will be to give the nation a look at his heart as well.
Forty years ago at the convention in Chicago, the whole world was watching. It is again.