Edit: I am actually a native speaker of English, and I know that "whom" is not often used these days. However, the reason I am asking this question is to better understand grammar, so that I can compare and contrast English grammar with the grammar of French (a language I am trying to learn).
Suppose I want to speak English in a register that still uses the word "whom".
I understand that we use the word "who" if "who" is a subject:
Who ate my sandwich?
and that we use "whom" if "whom" is an object:
On whom do you have a crush?
But I'm confused which word I use in the following response about Marc, because the person I'm referring to with "who(m)" seems to be both an object and a subject:
-- Who are you hoping will choose you as their teammate?
-- It is Marc whom I want to ask me to be his teammate.
"I want Marc" makes Marc sound like an object; but "Marc asks me to be his teammate" makes Marc sound like a subject.
Questions: Do I use "who" or "whom" in the sentence about Marc? Why?