Ive been having the same problem since I bought my Durango. Sometimes it works ,sometimes not . Had to the dealer a number times and they changed the batteries on both keys , reprogrammed them . the issue went away for awhile and now its back

 

Do not keep the key fobs near your cell phones and don't put your cell phones near the dash board.

The RF interference can jack with the wireless keyless operations

 

And never leave the Keys in the truck

 

That's just the "baby manual". The full manual is around 694 pages!!

 

I also read somewhere that certain radar detectors can affect the push botton start something to do with interference between the keyfob signal and the dash. If you have one try removing it from the truck for a while see if you're issue goes away.

Sounds strange but I even recall installing HID lights on a Mercedes GL450 and when turned on I got interference with satellite radio if I'm not mistaken. So anything is possible.

But my first guess is it sound more like the button isn't going down far enough since you can push it to start without the actual button.