Fatal mistake?

The novel several times makes the point that Vito never uttered a threat, not even to enemies, and he instructed Tom to do likewise. A wise policy. But, Michael, in Sicily, gratuitously threatens Sr. Vitelli in his cafe when Vitelli wants to know who he is and what he wants with his daughter :

"I am an American -- hiding in Sicily..My name is Michael Corleone...There are people who'd pay a lot of money for that information...But then your daughter would lose a father......instead of gaining a husband."

That's a hell of a way to introduce himself to the father of the girl he's just been smitten with, and who he's depending on to get an invitation to visit his daughter. More to the point: it's a self-fulfilling prophecy. How could he keep that info fro spreading all over a small Sicilian town where everyone knows everyone else, ]and they're probably related, too? The threat made him sound (perhaps intentionally) like a big-time American gangster.

He also agreed to a very public wedding (while "hiding in Sicily"), with the whole town invited. Naturally, people were going to ask Vitelli about his daughter's bridegroom. What was he going to say, "He's some cretino from somewhere who fell for Apollonia while he was taking a nature walk with these two lupara-toting bird-watchers"? Small wonder that word got back to Barzini, who got to Fabrizio.

As you have said [or similar!] many times, Turnbull, when blinded by revenge and greed it can affect the judgements of even a master manipulator like Michael

Let's add lust! to revenge and greed

TB, Michael was more powerful than Vito, but lacked Vito's finesse when using that power. I found his words spoken to Vitelli to be quite awkward and unnecessary. As you point out, his subsequent behavior and wedding plastered his name across Sicily.

I always reckoned the Thunderbolt was lust not love

He could have stopped at "I am an American and I reckon that may have still got him what he wanted

No doubt the big-time American gangster talk
1. got Vitelli's attention and an invitation to his home
2. got the brothers to put away their shot guns
3. got Apollonia
4. sadly lost Apollonia too

Vito threatened the band leader Luca Brasi holding a gun to his head, brains or signature

Vito came very close to breaking that policy once..... in the meeting of the dons when Vito announced, "My youngest son -- was forced to leave this country, -- because of this Sollozzo business. All right -- and I have to make arrangements to bring him back here safely -- cleared of all these false charges. But I'm a superstitious man -- and if some unlucky accident should befall him -- if he should get shot in the head by a police officer -- or if he -- should hang himself in his jail cell -- or if he's struck by a bolt of lightning -- then I'm going to blame some of the people in this room. And that, I do not forgive".

That's a threat to my way of thinking.

Well technically he didn't specify car bombs.... So car bomb loophole? Just kidding. What strikes me about this is that the threat seemed to fall flat with Barzini. An attempt was still made on Michael's life, killing Vito's daughter in-law (and unborn grandchild) in the process. Much more overt than a fake suicide. And then the Corleones just sit on it.... for 5-7 years? Of course, we know that was an act but still.

I believe the film has Appalonia's death BEFORE the Don't meeting. While the novel states Vito was surprised Barzini took another shot at Michael (when discussing Fabrizio). For the novel timeline, it states it took Vito a year from the meeting to get Michael home, and that it took Michael 3 months from her death to make arrangements. So at face value, that means ~9 months after the Dons meeting.

(I know I know, trying to reconcile timelines is difficult at best)

That may be the understatement of the year, UJ!

From the film, the sequence appears that 1) Sonny is killed; 2) Vito is told that night, says "This war stops now," and orders Tom to arrange a meeting of the heads of the Families; 3) Don Tomassino tells Michael sometime (but not a lot) later that Sonny was killed, and he has to leave for Siracusa "subito";
4) Apollonia is killed when the car that, presumably, was going to take them to Siracusa is blown up by Fabrizzio. I'm guessing that all of this transpired in less than two weeks.

But, it probably took more than two weeks to arrange the Commission meeting, so Barzini's attempt to use Fabrizzio to kill Michael didn't violate an agreement with Vito because there was no agreement at that point. Barzini may even have gotten the idea of killing Michael after he was notified that Vito wanted a meeting in order to further weaken Vito's position at the actual meeting, On the other hand, Barzini could have started arrangements to have Michael killed before Sonny was killed.

As usual TB, your analysis is pretty good. Yes, we don't know when Barzini conceived of murdering Michael. After reviewing the transcript, I doubt Michael's murder was planned after the Don's meeting. The transcript does not provide a timeline, but the transcript sequence has Tommasino visiting Michael right after Vito visits with with Bonasera which indicates that Sonny's death and the attempt on Michael happened right after and before the Don's meeting.

It had to have happened in between the time of Sonny's death and the meeting. Don't forget this all took place in the late 1940's or early 1950's. It would have taken a while for the word to get from New York to Palermo to the Sicilian countryside that a deal was struck and Michael was not to have been touched. Turned out to be an interesting outcome for Kay.

DT, welcome back!

Hey DT. Where you been?

Welcome back, DT!

I agree that we shouldn't overlook the time lag in communication back then. I don't recall seeing any telephones (or telephone lines) in the Sicilian scenes. Even if the hit happened after the meeting, it's unlikely that Barzini easily get a message to Fabrizio to call off the plan.

It's also possible that Barzini didn't make it a real priority to call off the plan. He still wanted to be #1 and killing Michael would have furthered that plan, deal or no deal.