Sorry, but to rephrase the sentence, you definitely wouldn't say "We must blame he" . . . you would say "We must blame him"
I stand by my criticism. You don't even need the "to" to rephrase the sentence.
But I do except your apology.
Was that sarcasm? Sure looks like it.
Sorry, but to rephrase the sentence, you definitely wouldn't say "We must blame he" . . . you would say "We must blame him"
You would not say "We must blame to him" -- which is what you are saying when you use "whom" in "Whom we must blame for Boston."
But let me ping Tax-chick, who knows more than I do.
“Never apologize: it’s a sign of weakness.” (John Wayne)
“Whom must we blame?” “We must blame him!” “Whom” and “him” are both objective-case pronouns, even though “whom” has been relocated to the beginning.
If you want to think of the pronoun as the object of a preposition, you could phrase the sentences, “To whom can we assign blame?” “We can assign blame to him.” However, this is not necessary for us to need an objective, rather than subjective, pronoun.
(This grammar clarification has been offered in memory of “Nina0113,” who loved a good compound-complex sentence almost as much as she loved a needy cat.)