Green’s Dictionary of Slang

a dead certainty, usu. in political use, also attrib.

1939		S.F. News 30 Jan. 15/5: Bear Cagers Appear Shoo-In for Southern Division Title.
1948		Life 18 Oct. 44/1: Dewey looks like a shoo-in for the presidency.
1950		N.Y. Times 5 Mar. 2S/5: The Cleveland Indians [...] looked a shoo-in to repeat.
1952		N.Y. Journal-American cited in Walter Winchell On Broadway n.d. [synd. col.] WW had the Governor still rated a shoo-in with the Gotham gambling fraternity.
1964		H.S. Thompson letter 24 June in Proud Highway (1997) 457: If they’ll consider Joe Benetiz, I should be a shoo-in.
1976		R. Sabbag Snowblind (1978) 107: A shoo-in. Uta would carry the coke.
1983		T. White Catch a Fire 263: Manley was a virtual shoo–in [for election].
1987		Kid ’N’ Play ‘Last Night’ 🎵 Getting paid would be a shoo-in.
1996		Eble Sl. and Sociability 21: The argot of the race-track, for instance, is responsible for piker ‘small time gambler’; ringer ‘illegally substituted horse’; shoo-in ‘fixed race, easy win’; and others.
1996		P. Beatty White Boy Shuffle 162: With grades and test scores like these [...] you’re a shoo-in.
2000		Observer Mag. 19 Mar. 16: Martin Creed [...] is a shoo-in for this year’s Turner Prize shortlist.
2003		Bug (Aus.) Sept. 🌐 It’s a shame that Dally M was called off as, if Bunny won, he had to be shoo-in for induction into the Dickhead Ball of Flame.
2005		Guardian G2 5 May 4: He’d be a shoo-in for the next governor of New York.
2010		K. Richards Life 371: Ronnie [Wood] wasn’t necessarily a shoo-in as out new guiarist.
2017		Star Democrat (Easton, MD) 22 Feb. A7/1: In normal times it would be a shoo-in for the Labour Party.
2023		(con. 1962) J. Ellroy Enchanters 185: [S]he blathered on about herself as our ‘shoo-in’ First lady.