In watching GF1 last night on TCM, a question occurred to me:

Why did Tom say to Sollozzo that even Sonny wouldn't be able to call off Luca Brasi?

It seems to be very out of character for Tom to say something like that in general, and all the more inexplicable since Luca was pretending to be dissatisfied with the Corleones at that point. (Actually, he was dead, but Tom didn't know that.)

Was this just a mistake on Tom's part, or was there some angle he was working?