How much substance will Obama offer?
It is hardly a disadvantage for a politician to be a brilliant, charismatic speaker. But it can have a downside if they are wheeled out, or wheel themselves out, as the ultimate big gun when each crisis looms.
I well remember covering Tony Blair's annual conference speeches. Most were well-crafted, clever, even moving.
But as the years passed, it became clearer that where the words were detached from action they only encouraged cynicism in all but the faithful.
His staff were equally cynical. "Is it the most important speech of his political life?" some breathless hack would ask. "Yeah. Since the last one. Until the next one," an aide would reply.
Conservatives are warning that Mr Obama must not come on tonight with the same old, same old, but must offer substance. Jonah Goldberg puts the case with ferocious humour.
The president has recognised that what has been lacking is clarity. We have already got some extracts from the speech and he is going to say that the health care system is at breaking point.
He will blame partisan scare tactics, bickering and games for confusion around the issue. He will promise those with health insurance that nothing in the plan will mean they have to change what they have got, and promise those without insurance that they will have quality, affordable choices.
And that "public option" that worries so many on the right? It is not in the partial extract I have seen, so watch this space (literally) to find out what the president has to say on the subject.
Will the substance and the rhetoric be enough? I will be blogging live, minute by minute...