Most short-term travel medical policies only cover you while you are outside the US and are very limited to the amount of coverage for any follow-up care after you return to the U.S.  If you are injured or diagnosed with a terminal illness and do not have adequate U.S. health insurance, then you run the RISK of being uninsurable and the possibility of paying medical expenses out of pocket.

Purchase the Global Citizen and be covered in and out of the U.S.