This site takes a guess at what each of the three remaining presidential candidates might look like after being in office for four years. The idea being that the stresses of being president take a toll on you physically and cause you to age more quickly.
I kind of think they’re overdoing the aging effect of the office on Obama and Clinton. McCain is already up there so there’s not a lot of room for additional aging. It looks like they mostly just added some age spots to him. I’m not sure I even buy the premise. I think most presidents age rather naturally during their time in office.