Green’s Dictionary of Slang

(US) any chance situation involving three components.

1996		P. Temple Bad Debts (2012) [ebook] Danny was going to hill you that night. You and Scullin and Ronnie were the trifecta.
2001		(con. 1964–8) J. Ellroy Cold Six Thousand 90: Horse/weed/cocaine — verboten. The fuzz enforced the trifecta.
2013		D. Whish-Wilson Zero at the Bone [ebook] The boozer’s trifecta, old mate. Emphysema and lung cancer, some pretty bad cirrhosis in my liver.