My understanding is that "listening" to communication between Trump and a foreign national would not require a FISA warrant. I say "listening" because, I believe, all communications with foreign nationals are recorded but only some are actually listened to by actual people.
No, the straw man argument is that we can tell whether Trump was wiretapped by the presence or absence of a FISA warrant.
The president does not sign FISA warrants, the entire purpose of FISA is to streamline (almost to automate) the issuance of warrants.
https://en.wikipedia.org/wiki/United_States_Foreign_Intellig...