How could his staff not have checked...he always hires "the best people"!
Also, if you know your mic is hot, there is a solution, you move it away from your mouth a little bit. Move the mic or reposition yourself. Those weren't fixed mics. At that, from a lot of the images I'm seeing, it looks like he was leaning in on the mic, so it coming across as hot may be his own fault for how he was standing.
![](http://eaworldview.com/wp-content/uploads/2016/09/TRUMP-CLINTON-DEBATE-26-09-16-e1474959304145.jpg)