Leaking p-trap joint and can't unscrew nut

I replaced my kitchen sink and garbage disposer and intended on swiveling the p-trap to line up with the new disposer. I thought the p-trap was attached with a slip joint connection and all I would have to do is loosen the slip joint nut. However, the nut won't move. I was still able to swivel the trap slightly, and of course now there is a drip coming from that joint. Any recommendations on how to fix? Thanks.

IT is a "union nut" not a "slip joint" and they are often very difficult to loosen, and often when you do the nut cracks. Since it is a union joint, "moving" it does make it leak unless you can tighten the nut further, or take it apart and use a suitable joint compound on it.

Thanks for the clarification. Since I don't think it can get any tighter, should my next step be to try turning the union nut (counterclockwise?) with Channel-Locks until it either comes loose or something breaks, and then go from there?

The nut is captive on the U, so the male threads are on the wall elbow. Make sure you are turning the right direction.

You can try it, but I would just cut it off and redo the whole thing using tubular trap and fittings instead of sch. 40 glued ones.