https://www.newyorker.com/magazine/2018/04/30/trump-giuliani-and-all-the-presidents-lawyers

“sine qua non.” = an essential condition; a thing that is absolutely necessary.

And yet, in the disparate cases, one can already glimpse a clear theme: Trump’s disdain for legal limits and, perhaps more dangerous, his almost uncanny ability to draw others into his vision. Comey writes in his memoir that, in a White House where lying, or remaining silent as the President lies, is considered an essential act of loyalty, he could “see how easily everyone in the room could become a co-conspirator to his preferred set of facts, or delusions.” Michael Avenatti, the lawyer for Stormy Daniels, whose proper name is Stephanie Clifford, told The New Yorker that he regards her case not as a sideshow but as a “sine qua non.” Avenatti, who is clear-eyed about the uses of publicity, is eagerly envisioning himself sharing headlines with Giuliani as the legal actions converge. What distorts the President’s judgment, Avenatti says, is “a misconception as to the importance of loyalty, or perceived loyalty.”