Guts.

I was assigned to a F-105 fighter bomber wing flying out of Korat Thailand during the Viet Nam war.  The day I arrived on base, we lost a Thud in combat.  For the next 90 days, my wing lost a plane every single day.  We saved some of the pilots, (never enough, but better than nothing).  Despite the risks from AAA, SAM, MIGS, and the unreliability of late 1950's jets, twice a day the pilots climbed into the cockpits and took off for North Viet Nam (route pack 6 we called it).  That took real guts.
  John McCain was shot down in the year I was over there.  He was flying off aircraft carriers which is even more dangerous than operating off the 10,000 foot concrete runway we had at Korat.
  I heard The Donald had spoken disparagingly of John McCain the other day.  I don't approve.  In fact, it makes me think that the The Donald shoots off his mouth too much to be President of the US.