Opinion by Matthew Dowd, ABC News Political ContributorSitting in Denver at the Democratic Convention and for me it's a bit of a surreal experience attending as member of media.I have been involved with operations and planning at two Democratic conventions (1988 and 1992) and two Republican conventions (2000 and 2004), and so this is a tad weird. For me, the most successful conventions communicate a broad and consistent theme and message that spans across all four nights.It's like a four act play where each act can have its separate dynamic and actors but the sum total of the entire four acts need to tell a dramatic story. And the speech by the nominee on Thursday night is by far the most watched and most important part of a convention.In 2004, John Kerry did not do this well and came out of the convention with little or no bounce and never had a consistent message going into November. George W. Bush on the other hand had a consistent thematic that ran through the convention and stayed disciplined throughout the fall campaign. So, we had the first night of this Democratic Convention and lets try to evaluate the night in the context of a four act play even though we are only 25 percent there.The Kennedy moment last night was very emotional and very passionate and you could feel the sense in the hall of real drama. Very good way to begin a convention with a little kick of passion. It's funny -- as I was watching the first day of the convention, I thought that this was like a 4x400 relay. You save your best sprinter for the last leg (Obama) and you put the sprinter with most energy in first leg (Kennedy) and you put your experienced sprinters in leg 2 and 3 (Clintons and Biden). Michelle Obama did an unbelievable job –- as good a speech by a potential first lady as I have ever seen or heard. She connected well with the crowd and I think we will see that she connected well with the mass audience. And the moment with her kids and Barack was priceless.But here is a concern I think Democrats should have: I didn't come away from the night with any consistent message or theme. It felt like it was multiple messages and points being made, but nothing that someone riding down the elevator could hold onto and communicate to someone in ten seconds. That's the sign of a good message.And looking at the three nights to come I get a sense each night has a different message and within each night there appears to be multiple messages, but I don't know what the broad theme is or what exactly the Democrats want this election to by about. And, folks, that's a problem.We could see this fixed by Thursday night and Obama's speech will be key, but after day one I am still struggling to know what the elevator speech is.