I was asked this by another accountant, and I'm having a major brain fart for some reason...

68 year old client with wife 60 years old.  He's wondering how much his wife can take out of her Roth IRA before it causes more taxes to be taken out of his social security.  I'm under the impression it wouldn't, because roth ira distributions wouldn't affect social security at all, because they're not taxable, but am I missing something?