In Mank (2020), Herman and Sara later attend an election night watch party at the Trocadero Nightclub. He wants to go double or nothin' on California Gubernatorial election to which L.B Mayer reacts on it:
L.B Mayer: You really will bet on anything. Keep your money. I'm happy enough just to nail that utopian son of a bitch to the wall.
Thalberg turns to Mank and says:
Thalberg: I told you. Your obligation was canceled out of gratitude.
What "obligation" did Mank made ?