[quidnunc]

For purposes of comfort he may have been wearing a vest with a front panel only because he was facing the audience all the time.

The picture above is from the second debate and if you know what to look for you can see the outline of the vest's back panel.

[Huntress]

Are there different thicknesses/strengths of bullet-proof vests for different purposes? The only bullet-proof vests I've ever recognized are the ones worn by highway patrol troopers in uniform, and they are so bulky that even my untrained eye can spot them a long way off.

[stylin19a]

I believe you are right. Something like this ?