What could have changed my Chihuahua's behavior?

I have a year old chihuahua. About a week ago, his attitude changed towards my husband and son. He nips at them and doesn't want to play with them. In the mornings, my husband takes him out to potty before leaving, but the last couple of days he has been nipping at my husband from his crate. There is no abuse on their part. In fact, my husband babies him more than I do. He will get up and sit with my husband and let him pet him. His attitude towards me is fine if not a little too clingy sometimes. He is eating and drinking well. He is pooping and peeing, too. He doesn't act sick (i.e. sleeping all the time, not eating). Any advice? What may cause this? How do I change this behavior?What could have changed my Chihuahua%26039;s behavior?
puppy preschool!What could have changed my Chihuahua%26039;s behavior?
second hand smoke. They blame everything else on that, so there you have it.What could have changed my Chihuahua%26039;s behavior?
Maybe your husband step on the little guy