In his defense, Tom tied to stop Sonny but he left in such a hurry. And with Genco said to fear Fanucci.. everyone except Vito did, even Clemenza and Tessio. It was when Vito sees the young hoods cut Fanucci that he realizes that Fanucci is nothing to fear. Genco was all brains and no strength. I wish Genco was in the films a little more. If you had never read the novel then you would have little knowledge of Genco.