Bill Murray was NOT Miscast
There seems to be the idea around that DeNiro and Murray should have switched roles in this film, with DeNiro as the scary mobster and Murray as the nice timid mouse who roars.
And evidently DeNiro was offered the mobster role first but wanted "the mouse."
All well and good -- DeNiro has always had a talent for playing low-key and mumbling(see: Jackie Brown) as much as savage.
But its harder for me to picture Murray playing the mouse.
Murray had built his star career on comedy -- but a kind of brash, all-guy comedy where he was the Alpha Male. He's a leader of men and a getter of girls in Stripes. He's the leader in Ghostbusters, too, and though the girl(Signourney Weaver) resists his goofball advances at first, she relents eventually. Murray played Hunter Thompson in a movie. Even his Caddyshack idiot had his tough side(as in advising Chevy Chase how he can cut a rival golfer's hamstring with a knife to cripple him.) Murray played bullies in Scrooged and Groundhog Day(before they turn at the end.)
In real life, Murray developed a tabloid reputation as a fairly mean guy, a brawler(he once fought backstage with Chase when Chase returned to host SNL) and he's tall and brawny enough to suggest a real talent with the fists.
Thus Murray was fine casting -- if not perfect casting -- to play a Mafia hood in Mad Dog and Glory. He brought all his innate danger and latent meanness to the role.
And as written, Murray had the goods that a Mob boss always needs: eventually we have to see WHY this guy is the boss, the top dog, the leader. In his first scene as a convenience store robbery hostage, Murray NEVER shows fear, he spits in the robbers face(I'm reminded of Pacino's Scarface facing down a chainsaw execution with similar defiance.) As the film goes along, Murray's boss reveals his power-mad cruelty("I OWN her!" he yells of the woman DeNiro loves.)
And then finally, Murray reveals something I think a lot of mob bosses likely have: the Alpha Dog ability to beat others on their team up. When Murray starts punching DeNiro, hard, I BELIEVED the power of those punches. Somebody trained Murray well.
I'm reminded that an even more nerdish comic -- Albert Brooks -- gave us a vision of a mob boss in "Drive" that showed his character was willing to stick a fork in a man's eye in anger before slashing his throat -- Murray didn't have to go THAT far. But Murray's tallness, his sullenness and his excellent punch made the case for a most believable mob boss.
He wasn't miscast at all.