I agree that both Clinton or Trump are not the best candidates and that some other, like Sanders or Cruz, or Kasisch, was better candidates.
But, through democratic process, Trump and Clinton have won and remained in the race.
US President is very important person but most of his decisions he can't make alone, without US congress.
Also, he has advisers, ministers, in his administration and they work as team.
So, even bad President eventually can become good president if he hire the right people to work with him
Don't worry about America, they will be fine, more or less.