What would cause a car door not to align with the strike?

You need to replace the pins. Although answer 1 is not incorrect, it may not be necessary to make the drastic move of removing and replacing the hinge pins. Usually the reason for replacing hinge pins is excessive wear of the pins, and also usually if the pins are THAT badly worn, so also are one or both of the hinge brackets through which the pins pass. This condition dictates total replacement of the entire hinge. BEFORE REPLACING ANYTHING, I suggest trying to ADJUST the door/hinges. The door hinges are bolted to the door post with 3 to 4 bolts or large screws per hinge. Try adjusting by: 1. Open the door, and locate the hinges and examine the area right around the hinge. Sometimes, if the hinges have "slipped," you can see an "outline" showing where the hinge WAS located. Visual confirmation of slippage not withstanding, continue this adjustment procedure. 2. With the proper tool [a wrench, or a screwdriver] LOOSEN[only] the bolts or screws [all fasteners] on both hinges. Only loosen JUST ENOUGH to allow [when the door is almost closed, to within an inch or two of the latch post]to be lifted into proper alignment in the opening and with the strike/guide. 3. While holding the door at the proper elevation, carefully open it just enough to retighten the fasteners. There WILL be a tendency for the door position to shift on you, possibly requiring several attempts. However, with patience, you may be able to readjust the door, and prevent the need to replace the pins and/or hinges.