FROM ANOTHER WEBSITE. INTERESTING...
Motive: Butch is likely to be new boss of NY, and remember how he gave up Phil in a heartbeat so he could rise to the top... you really think he's gonna forgive Tony for sticking a revolver in his face: "how about I put a bullet in your fuckin head?!". Plus it'd be a huge liability to leave Tony alive when he knows about Butch's disloyalty, if New York found out it could cost Butch his life. So Butch allows Tony to kill Phil and then takes out Tony in what looks like retribution, so he comes out as the Boss of New York, smelling of roses with no loose ends. (I believe Paulie is the other loose end, which'd make his death is imminent, just like he fears. IMO the cat represents/brings death, obsessively purring at the photo of a "dead kid", Chrissy. It almost supernaturally appears outside Satriale's at the end of a conversation where Paulie states his reluctance to take on a cursed position which has gotten everyone else killed).
But hey, if Tony didn't die he's fucked anyway. He was told by his lawyer that he has a 80%-90% chance of being indicted. And they don't even know about all the snitching we've seen over the years.
Longest post I have ever/ will ever type. Oh, 'Don't Stop Believing', right?!