The company's challenges might not be insurmountable, but they are serious enough to warrant a healthy dose of skepticism.Tandem Diabetes Care (TNDM 0.38%), a medical device company, has had a rough year. The company's shares are down by 43%. It might be tempting to consider the stock at current levels. If it can perform well over the next few years, initiating a position today would yield excellent returns in the medium term. However, several factors need to align for Tandem Diabetes Care to become an attr ...