This is from the BBC Tomato shortage
"Tomato shortage: How far is Brexit to blame?"
At first I could not quite decide what exactly the question is focusing on. I thought people have not yet understood that the problem was actually caused by Brexit, so it still seems a little bit far away for people to come to understand it.
However, as I read, I understood that the text was trying to reveal *how much of the problem (tomato shortage) is caused by the Brexit.
Then I start to think about the question and I tried to adapt it to find out the share of someone in any problem in daily life. As a non-native speaker, if I was to form a question to find out "how much is someone - amongst others- can be held responsible for a problem, I would not be able to form the sentence by using "how far".
I would probably form the sentence like one of these;
"How much of the blame is on him?" or
"To what extent can he be blamed?" or
"How much of it is because of him?" or
But since I am a non-native speaker, I can not decide whether or not these would be as idiomatic as "How far is he to blame?"
Would they be? Or Is "How far is he to blame?" the only way to ask about it in an idiomatic way?