grammar - Is this grammatical: 彼は映画スターであり、政治家もだ。

I was about to ask a question but I can't without first confirming,

Is this sentence:

彼は映画スターであり、政治家もだ。

grammatically correct, and mean:

He is a movie star and also a politician.

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^{Follow-up question here: Why does replacing だ to である changes the meaning of a the sentence?}

Answer

Recall that だ is the contracted form of である.で has to be attached to a noun. You can't leave it behind も as もである. So the correct way of inserting も will be:

彼は政治家でもある

You might be wondering whether で before も can be omitted. Only arguments can have the (case) particle omitted before は or も. In this case, the noun 政治家 is a predicate, so you cannot omit で before も.