Laudator Temporis Acti

Cameron Hilditch, "How Critical Race Theory Works," National Review (May 8, 2021):

The most important question to the critical theorist is therefore Cicero's famous "Cui bono?" — "Who benefits?"

Cicero himself attributed the phrase to Cassius Longinus. See Robert Ogilvie, Horae Latinae: Studies in Synonyms and Syntax (London: Longmans, Green & Co., 1901), p. 76:

"Cui bono?" is the well-known test of Cassius Longinus (Consul, B.C. 127) for discovering the author of a secret crime, — to whom is it for a benefit? who is the gainer by it? cui being the person, and bono the thing. The phrase is often misquoted, as if cui agreed with bono — to what good end? what purpose does it serve?

Rosc. A. 30 L. Cassius ille identidem in causis quaerere solebat, cui bono fuisset.
Rosc. A. 5 accusant ii quibus occidi patrem Sex. Rosci bono fuit.

Rosc. A. is Cicero's speech Pro Roscio Amerino. Cf. also his speech Pro Milone 32.3 (... illud Cassianum 'cui bono fuerit?' ...)

On the double dative see Charles E. Bennett, A Latin Grammar, rev. ed. (1908; rpt. Boston: Allyn and Bacon, 1913), p. 133 (§ 191, 2, a):

The Dative of Purpose or Tendency designates the end toward which an action is directed or the direction in which it tends. It is used—

    [....]

    Much more frequently in connection with another Dative of the person:—

      Especially with some form of esse; as,—

        fortunae tuae mihi curae sunt, your fortunes are a care to me (lit. for a care);

        nobis sunt odio, they are an object of hatred to us;

        cui bono? to whom is it of advantage?