Trump was classified as fit for duty in the US Armed Forces in 1964 when he turned 18. Like every other boy, his name was entered into the draft for military duty. In 1969 when the first lottery to determine the order of how young men were selected from those on the eligible for service rolls, Trump was given the very high number of 580. There were two lotteries that covered the Vietnam war period. The LOWER your number the more likely you were to be called. The highest number called from the first draft lottery list was 180. The highest number called from the second draft lottery list was 320. In other words Trump the coward was NEVER in danger of being called for military duty.
After each lottery list was pulled and each young man given his number, it was possible to apply for various exemptions to avoid military service. Like many other men, Trump obtained a normal deferment for the time he was in post-high school education. This was normal and not improper. In 1968 when Trump was 22 years old, he "obtained" a letter from a doctor saying he had bone spurs on his heels.
Even though Trump the coward must have known his lottery number kept him safe from ever being called to duty he still obtained a 4F medical deferment for the duration of the Vietnam war. Bone spurs are very painful and only become more debilitating as a person ages. Watch for yourself as POTUS walks, you will see no sign of pain or problems walking with bone spurs.
Further more Trump could have entered the ROTC, of which he was a member, and received an ADT ( Active Duty for Training ) classification. This would have guaranteed he never would go to Vietnam but would allow him to meet his military obligation. All he would have had to do was go to Basic Officer course, depending on what branch of the military he chose. Some of these courses were approximately 6 weeks. Then he would have been in the US Army reserve on home station duty, requiring only 2 weeks a year and one weekend a month of showing up at the local Army reserve post.