In 2008, I was really torn between voting for Hilary Clinton or Barack Obama in the primary. I made up my mind when I read that the Clinton campaign was running out of money about half way through the primaries. Apparently, they had planned for a short campaign, expecting to build up an overwhelming lead early, while the Obama had planned for the long haul. That made up my mind for me because I figured that you can't be trusted to manage the US government if you can't manage your own election campaign. (And management matters. Compare, for example, the federal responses to hurricane Katrina and hurricane Sandy.)
Now, I know that the President doesn't really manage the government, and the candidate doesn't really run the campaign, either. But the candidate picks the people who manage the campaign, and the President picks the people who pick the people who manage the government. So the quality of the people who run the candidate's campaign is a good indication of the quality of people who will be running the country if that candidate is selected.
For that reason, not only was I worried about Mitt Romney's ideology and politics, but I was also worried about his ability to manage, because it was clear his campaign was being poorly run. It wasn't just the frequency of his campaign wandering off-message, but also the inability of his staff to anticipate and be able to answer questions that were obviously going to be asked sooner or later. (The most famous example was a telephone conference called for the purpose of talking about women's issues in which senior Romney staff were unable to say whether or not Romney supported the Lilly Ledbetter Fair Pay Act.)
Now I read (in RedState.com of all places) that it was actually worse than I thought: "Campaign Sources: The Romney Campaign was a Consultant Con Job."