Identities are masked when a US person who is NOT the target of the surveillance is captured on the communication -- this is an "incidental communication." They are unmasked when the identity is necessary to understand the intelligence. All legal, no warrant required. https://twitter.com/Breaking911/status/1260646396216012800

In requesting an identity be "unmasked," you by definition don't know who it is so you can't be politically targeting a specific individual. And if the claim is that Flynn's role in the transition made his actions "legal," you are conceding that his identity is relevant.