You will be fine. The odds are that you will get through in 90 minutes -- if not, Delta will put you on the next available flight.

After you go through Customs, but before you hit the TSA line, you will drop off your luggage. If you see that you have enough time left, just leave it on the belt. If not, ask a DL rep to re-schedule you.

Should you find yourself delayed by an unsually long (slow) TSA line, go to the first DL rep after Security and ask for the re-schedule. (It is preferable to do it first only to be certain that your bags go on the same flight as you.)