The other day the Hillary Clinton campaign issued a press release attacking Barack Obama for being ambitious, and managed to dig up a third grade essay he wrote. I think it is preposterous to criticize Obama for this. When we are young, and even in college making life plans, we all have ideas and dreams as to what we'd like to be when we grow-up. They are not all serious. When I was in first grade I wanted to be an astronaut.
In spite of all this, having worked on campaigns and such, people do not normally get elected by accident. It's a lot of work to be a candidate, and you need to want it if you are to get elected. Of all the issues and differences between the candidates in this campaign, I find this one to be rather petty. If you are running for an office, including President, there is always going to be a component of ambition there.