When Michael arrives at the hospital to visit with Vito, he finds that there is no one there guarding his father. When he questions the nurse she informs him that the police made all of the Don's 'visitors' leave about 10 minutes ago. So he makes the call home and informs Sonny that there is no one at the hospital to protect Vito.

My question is this;

How is it that none of the Corleone people who were at the hospital were able to get word back to the Corleones that Vito was left unguarded?

And if it was a matter of the bodyguards NOT being able to make the phone call because they had been arrested, then how come one of the policemen on the Corleone payroll, or someone within the hospital itself didn't inform Sonny & Co. that McCluskey had rounded up and arrested the Corleone bodyguards?

In theory, as much as I liked Sonny, he was negligent in that he had not taken EVERY precaution necessary to make sure that his father was and would remain protected. Sonny had not covered all of the bases to insure that if something were done to compromise the Don's protection, there would be someone on the Corleone payroll from both the hospital and the police department to immediately let him know.