The tree is leaning now and it wasn't before — what should I do?

A lean that was not there last week. At the base: fresh soil cracks in a curved arc, a mound or heave of turf on the side opposite the lean, sunken soil on the lean side, exposed or snapped roots, split mulch rings. Sight the trunk against a fixed reference like a fence post or the corner of the house — that comparison is more reliable than your memory. Root-plate failure already underway. The tree is not leaning; it is falling slowly, and the remaining soil grip is the only thing still holding it. This is categorically different from a tree that has leaned for years toward light, which has laid down reaction wood along the compressed side and is genuinely stable.