What to do about a gap between the floor and walls in the house?

I thought it needed molding, but there is molding already, so maybe the floor is sagging, and we haven't noticed in the year we've lived in this old house. So the existing molding doesn't reach the floor anymore. (Quite a neat levitation trick). So what's the bet way to deal with this? Sealant under the walls gets messy and uneven. Thanks.