The word used for those, (either he or she) that does not do what is needed of him or doesn't follow all the way through eg. half-asses it, thus committing Halfassary
To perform an act in a manner characterized by lack of give-a-shit, by absent-mindedness, or by disregard for quality of work; determined by or dependent on apathy; careless.
Wow, Donald is really planning his political campaign halfasszardly, but it seems to be working for him.