All three of them avoided the draft? Kin gaylords. Mind you, says a lot about the american people voting in cowards as their leaders.....
It was not an existential threat like World War 2, or even a UN approved war like Korea. It was a war of choice for the Americans, but with no clear objectives or end in view.
Those with the means could and did arrange their lives to avoid the draft- often with the connivance of their local medics.
Those without means, the poor, and uneducated, tended to get swept up, whatever their colour.
Clinton got an educational deferment, Bush served in the National Guard, (and the Americans do make more use of NG than we do), but Trump simply lied.
(No surprise there).