His first work on federalism was the collection Federalism , Mature and Emergent , which he edited .
Late in his career , MacMahon developed an interest in federalism , publishing three books on the subject .
MacMahon 's first work on federalism was the collection Federalism , Mature and Emergent , which he edited .
Late in his career , MacMahon developed an interest in federalism , publishing three books on the subject .