This corroborates earlier reports from Lorne Michaels, who has also explained how the gig came about.
Alec Baldwin spent a lot of time getting to this admission on Jimmy Kimmel Live!
Despite this explanation, even Jimmy Kimmel seemed genuinely shocked to hear that Alec Baldwin’s impression wasn’t a done deal on the day it first aired.
That could have literally been a disaster, so I guess we’re happy that it all worked out for the actor.