Glue and clamp it. You may want to install longer screws where the latch and deadbolt go into the door jam for added security if you have not done so already. I used 3.5 inch screws on mine so they bite all the way through the jam into the house framing.
If you are going to glue and clamp, you could add in some trim screws to pull the joint together. They have a very small head with a square drive. I would pre drill a slightly smaller hole than the trim screw just to make sure it doesn't cause the wood to split.
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