Can a short-term policy turn me down if I have a pre-existing condition?

Yes.  In general, the application for short-term policies will ask questions about your current health status and your health history.  Depending on your answers, if you have or have had a pre-existing condition you might be turned down or charge more.  How short-term policies treat you also depends on where you live.  A few states have passed laws to prohibit short-term policies from discriminating based on health status.