Considering Olenna’s view on Renly’s claim, mainly that he thought he looked good in a crown and people agreed, do you think that explains Mace’s support. Maybe Renly used some of his charisma on Mace and convinced him that Stannis would back the Florents over them, may hold a grudge, or simply that it’d be easier to make him King over Mister Grump & Grudge?