Things have improved. Jack peed several times in his underpants or bathing suit today, but only a little at a time. When he sat on the potty he peed quite a bit, so it feels like he's figuring things out.
We had a gorgeous sunny warm day today, so we spent most of the day in the yard or on the deck. Jack went snail hunting and we picked our daily apple from our gravenstein tree.
He did poop in his underpants again, but it wasn't as messy as yesterday. We'll work on that tomorrow.
I do feel hopeful this evening.