The Don's Guilt...maybe?

Do you think the Don ever felt guilty...by ANY of his actions? The novel always reminds us that he felt he did "what he had to do" for his family.

I wonder if in the back of his mind he blamed himself for Sonny's demise. That is one of the first times he looks as though, after everything he had gained in life...power, money, respect...none of it mattered once he saw his son in that casket.

He regretted that he had to make Santino his successor, knowing all the while Santino would make a bad don.