Being president, is physically and cognitively grueling. Hence, the need for medical records and histories are parts of the vetting process - even for vice presidential candidates.
The correct approach to this issue, is more of a case of semantics. The precarious lines drawn between legitimate concerns and size discrimination can get skewed.
Unfortunately, one's physical appearance dose play a major role in today's society - health concerns not withstanding. I take the music industry as an example:
Before the age of MTV and YouTube, someone like Beyoncé, would've stood a chance, against the voice of an Aretha Franklin. Now, since everything is audio visual - more visual than audio, the Aretha's of today, wouldn't stand a chance against the today's Beyoncés'.
Granted, some will judge Chris Christie solely on his appearance, others on his abilities and some on legitimate health concerns. But fairness and pragmatism should be the role of the day. Who knows, he could turn out to be the political equivalent of an Adele!