I know several folks that are single issue voters. Most have are articulate and well-informed opinions, others not-so-much. These individual issues include: capital punishment, abortion, guns, taxation, animal rights and medical research. If I could set policy and positions aside, I would decide my candidate based solely on the graphic design of the campaign.
Design makes a statement. Design shouldn't just support a message. Design should convey a message.
McCain's campaign has one theme with a few variations on the design. As much as I have heard the terms "maverick" and "agent of change", the design doesn't speak that to me.
Obama's campaign design convinces me that it's something different. The design isn't without problems, but I find it compelling. I'm still not sure what to think about the "O" graphic. I assume it is a rising sun over and American flag, as well as the "O for Obama". I think will argue that the sun is setting or possibly the red stripes are an empty highway. Honestly, maybe Barack is for one egg sunny side up with three pieces of bacon.
If you happen to like political images there is an independent Obama site. McCain doesn't have an counterpart site.
Here's a NY Times look at why the Bush bumper sticker was superior to the Kerry bumper sticker.
Or here's a well-written historical look at political memorabilia.