'Where's John Wilkes Booth When You Need Him?'

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Legendary Broadway star Carole Cook said something so shocking when asked about Donald Trump -- "Where's John Wilkes Booth when you need him?"

Cook and her husband were leaving Craig's in WeHo Sunday night when our photog asked about a performance of "Frozen" last week, when a member of the audience unfurled a banner that read, "Trump 2020." An actor onstage ripped it from the guy's hands and threw it off stage.

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Cook clearly thinks more drastic measures are required, and the most shocking part is that she clearly knew what she was going to say. Based on her husband's reaction it's something they've said before.

Check it out ... her husband makes sure people know ... Booth assassinated a president.