I just went through this on my Dart....Same problem. First click was fine, could not make it latch on the second. It was a multitude of things.

1) Weather stripping is new
2) My door panels (early dart) were built too big and were hitting the weather strip
3) door was slightly mis aligned which contributed to the door binding on the weather strip. My doors were a little too far in on the pillar.
4)The striker needed a slight adjustment.

I was so mad at mine when I installed the weather strip and door panels I just went in the house. Both doors shut well before that. It took me several afternoons of tinkering about a week later and now they work great.