Laudator Temporis Acti

Kyra Haas, "No, Socrates didn't call slander the 'tool of the losers'," Politifact (October 8, 2018):

A viral image on Facebook quotes Socrates as saying, "When the debate is lost, slander becomes the tool of the losers."​

There's no evidence Socrates said that.

Joel Eidsath (per litteras) suggests that the substance of the quotation is contained in Plato's Apology. He adduces the following two passages.

Plato, Apology 21 b-d (tr. Christopher Emlyn-Jones and William Preddy):

Now consider why I say these things. It's because I'm going to tell you where my bad reputation comes from....So by examining him carefully—there's no need for me to tell you his name; he was one of the politicians who, when I investigated him, gave me this impression, fellow Athenians—and by engaging him in conversation it seemed to me that this man seemed to be wise both to a lot of other people and above all to himself, but he wasn't. Then I attempted to demonstrate to him that he thought he was wise, but wasn't. Consequently then I earned his dislike and that of many of those who were standing by....

Id. 22 e-23 a:

So as a result of this scrutiny, men of Athens, I incurred a great deal of enmity of a very harsh and grievous kind, so that from this there have arisen many slanders, and I got this label "wise."

The Greek:

Σκέψασθε δὴ ὧν ἕνεκα ταῦτα λέγω· μέλλω γὰρ ὑμᾶς διδάξειν ὅθεν μοι ἡ διαβολὴ γέγονεν....διασκοπῶν οὖν τοῦτον—ὀνόματι γὰρ οὐδὲν δέομαι λέγειν, ἦν δέ τις τῶν πολιτικῶν πρὸς ὃν ἐγὼ σκοπῶν τοιοῦτόν τι ἔπαθον, ὦ ἄνδρες Ἀθηναῖοι, καὶ διαλεγόμενος αὐτῷ—ἔδοξέ μοι οὗτος ὁ ἀνὴρ δοκεῖν μὲν εἶναι σοφὸς ἄλλοις τε πολλοῖς ἀνθρώποις καὶ μάλιστα ἑαυτῷ, εἶναι δ' οὔ· κἄπειτα ἐπειρώμην αὐτῷ δεικνύναι ὅτι οἴοιτο μὲν εἶναι σοφός, εἴη δ' οὔ. ἐντεῦθεν οὖν τούτῳ τε ἀπηχθόμην καὶ πολλοῖς τῶν παρόντων....

....Ἐκ ταυτησὶ δὴ τῆς ἐξετάσεως, ὦ ἄνδρες Ἀθηναῖοι, πολλαὶ μὲν ἀπέχθειαί μοι γεγόνασι καὶ οἷαι χαλεπώταται καὶ βαρύταται, ὥστε πολλὰς διαβολὰς ἀπ' αὐτῶν γεγονέναι, ὄνομα δὲ τοῦτο λέγεσθαι, σοφὸς εἶναι.

In other words, because Socrates' enemies were unsuccessful in debating him, they made slanderous accusations against him.