Q&A: My son was potty trained, but now seems to be regressing. Help!

It sounds like your son's message right now is "No, not yet," so backing off as you did is the right response. You may be able to teach him the "how" of potty training, but only he can decide on the "when". Any negative pressure tends only to set the process further back.

However, you can put a positive spin on the process and encourage him to train by letting him know your hopes. For example, talk up the idea that turning three entitles him to "big guy" status and that big guys use the toilet. Or, talk about how delighted you would be to see him train, without insisting that he do so. Since some of what he may be reacting to is the loss of his status as the baby of the family, emphasize that training is something he can do, whereas his new sibling can't even dream of such an accomplishment. As you see the readiness signs, keep up the positive encouragement.