This trend for the king to rely on his own men at the expense of the barons was exacerbated by the tradition of Angevin royal ira et malevolentia – "anger and ill-will" – and John's own personality. From Henry II onwards, ira et malevolentia had come to describe the right of the king to express his anger and displeasure at particular barons or clergy, building on the Norman concept of malevoncia – royal ill-will. In the Norman period, suffering the king's ill-will meant difficulties in obtaining grants, honours or petitions; Henry II had infamously expressed his fury and ill-will towards Thomas Becket; this ultimately resulted in Becket's death. John now had the additional ability to "cripple his vassals" on a significant scale using his new economic and judicial measures, which made the threat of royal anger all the more serious.
John had to additional ability to do what?
cripple his vassals