josh/donna post administration headcannons :)))
Oh gods, I am certain that piles of people smarter than me have covered this one, lol! Isn’t there a whole twitter world that built them a sparkly future?
But since you asked…
They get married during the first Santos term, and Donna is pregnant with their first daughter before the second one ends (it’s my headcanon, so of course he wins re-election). Therefore, post-administration they’ve got an incredibly independent toddler on their hands, and a second baby girl shortly after.
Surprising everybody but Toby, Josh takes over more of the childcare and becomes obsessed with exposing the girls to museums and dance lessons and every bonding activity he can think of–lots of hair braiding and nail painting and embarrassing photos that Donna holds for blackmail as needed.
Donna uses her clout as former FLOTUS COS to push for pet causes like criminal justice reform, and eventually reunites with CJ to co-found an NGO that tackles a wide range of progressive issues using the tactics CJ honed working with Franklin Hollis. Zoey Bartlet joins their staff, and becomes their daughter’s favorite babysitter–she even teaches them self-defense moves she learned post-abduction, making the Lyman-Moss daughters the safest ones on the block.
When the girls are in their teens, Donna decides to re-enter politics, this time as a Congresswoman. Josh amuses the press by running bake sales and holding photo ops and being the political spouse with much better savvy than he used to hold press conferences.
Their eldest daughter graduates top of her class and heads straight for law school.
Their younger daughter grows up to be President.