Every prime minister chooses when and where they want to expend political capital on effecting change. Unlike a departmental minister, they have some freedom about taking a risk with their own popularity and the fortunes of their party.
Andy Burnham has made his choice: social care. Driven in part by his personal experiences of his father suffering from dementia, and in part by an ambition to make the system work that dates back to his time as health secretary in the Brown administration, he has pointed the way.