My current dog did go through a brief period where he didn't think he had to "kennel up" into his crate in the car. We put a quick stop to that with a line on the collar then through the door of the crate then through the back of the crate. I gave him his command & corrected him into the crate. Once in, tossed him a treat, shut the door & verbaly praised him. After a few sessions he remembered he loved to jump into his crate when I asked him to.

I just wanted to add this is a very hard dog that recovers very quickly from a correction. I don't know if this is a good approach for a more sesitive dog.

I had an older dog that found rides in the car very uncomfortable. He wasn't a particular good car rider either, mainly had slight motion sickness. Drool galore.

We fixed this a few ways. First is we got him a car bed because he was older, very big (130 lbs), and having trouble with the hard floors on his joints. Second was we started going on short fun trips, like a mile to a park, or to my parent's place (they have 10 fenced acres he can run around on.) and that got a huge improvement on his refusal. Lastly I started taking a mid afternoon nap with him in the car. I found the key with him (he was a very soft dog) was making the car like a crate. Somewhere pleasant to be that was peaceful.
When my dear old Sam got really old and the weather got really cold we eventually got a heated cargo bed for him which was a huge hit. On cold mornings I could find him waiting by the car door to get inside to sleep on it.

I am an idiot!

I fed the dog breakfast in the car, it went okay, but he stood perched right on the edge of the trunk to eat.

I thought long and hard about how we seem to have gone from me nagging him to get in the car to him refusing in the last couple of days. I then thought about how he almost seemed afraid/spooked to get in the car the other night.

I decided to check the car kennel area. I though maybe he had barfed in there or had an accident (though he never has) and maybe did not want to go in there because it wasn't clean...

I found nothing.

I put him in the car today on my day off and looked back to back out of my driveway. I saw that his divider was very loose on one end and swaying into his area when I moved the car!!!!

I stopped the car and got him out. Now my dog is skittish about his personal space and I am quite sure that this metal devider swaying into him when I am driving on the bumpy snowy roads as well as when ever he bumps the bottom of it to lay down it would move and bother him too. I am quite sure this has caused the sudden increase in anxiety around the kennel.

In my feable defence the metal divider does make some noise when the car moves normally and it is dark when we leave and come home from work so I didn't notice it.

I fixed it, got him back in and took him for a ride, and a walk and he got back in the truck with no big issues!

He is soft and his memory long, but since he gets in the car every day, I am sure he will get over it.

I can now go back to improving my need to nag him to get in, but hope I won't have to deal with the outright weirdo refusal any more

I deserve a correction for being stressed and tired that day after work and not realizing that this sudden upping in anxiety in the dog probably had a cause

Not an idiot - good detective! I'm glad it was a simple fix.