Is potty training a rescue dog harder than potty training a new puppy?

There is no straight answer to this question as it depends on the situation and the individual. There are certain factors that are more likely to affect rescue dogs, but being a rescue dog doesn’t make them a victim of all or any of these factors by default, nor susceptible to the issue as an individual. The good news is, sans medical issues, every kind of dog can be potty trained.