Door won't close without slamming it

I was having trouble this spring. No matter how hard you slam the door it would not close until you pulled the handle a little. I went through and tightened all the screws associated with the door including all hinge screws for the main and screen door, latch system and even the screws holding the frame in the camper. After that it would latch if you slammed it. As I was doing all of that I also noticed that the goofy cheesy threshold cover had popped up over the lower part of the frame. I removed that and the door could be pushed closed with one finger. This left us with a tripping hazard so I went to Menards and got a 10' pc. of oak window trim that was the same height and countersunk some screws in it and it looks better than the factory