The only way is Pompey
At the end of the opening section of the speech (§§ 1-6), Cicero offers his audience a blueprint of the first half (§§ 6-49), outlining the three topics he feels he ought to cover (§ 6):
primum videtur de genere belli, deinde de magnitudine, tum de imperatore deligendo esse dicendum.
[‘I think it best to deal first with the nature of the war, next with its scope, and finally with the general to be chosen’.]
He then follows his blueprint to the letter. §§ 6-19 focus on the nature of the war (genus belli), §§ 20-26 on its extraordinary scale (magnitudo belli), and §§ 27-49 on the choice of the general. Cicero carefully marks the transitions from the first to the second topic, and then again from the second to the third (§ 20 and § 27):
quoniam de genere belli dixi, nunc de magnitudine pauca dicam (§ 20).
[‘Since I have spoken on the nature of the war, I shall now say a few words on its scope’.]
Satis mihi multa verba fecisse videor, qua re esset hoc bellum genere ipso necessarium, magnitudine periculosum. Restat ut de imperatore ad id bellum deligendo ac tantis rebus praeficiendo dicendum esse videatur (§ 27).
[I think I have covered at sufficient length why this war is both inevitable given its kind and perilous given its immense scope. What remains to be covered is that one ought to speak, it seems, about the general to be chosen for this war and to be put in charge of such important matters.]
Note how the satis multa at the opening of § 27 harks back to the pauca in § 20. Likewise, just as Cicero mentioned the topic just covered in § 20 (quoniam de genere belli dixi) before introducing the next (nunc de magnitudine pauca dicam), he continues with his careful signposting in § 27: first we get a review of what has been covered in the previous two sections, i.e. the genus and the magnitudo of the war against Mithridates; then we get a reminder of what still remains on the agenda (restat ut...), i.e. the choice of general. The first two items of Cicero’s tripartite structure, i.e. the nature and scope of the war, go together: both concern the war; the last item, in contrast, i.e. the general best suited for the job, is about the required personnel. The design is thus climactic.
If Cicero did his best to amplify the scope and danger of the war, he plays down any difficulty with choosing the general: there is only one! Given that Pompey lacks a plausible rival, the decision to put him in charge of this vital campaign, so Cicero claims, ought to be a no-brainer. He accordingly does not go on to weigh the relative merits of possible appointees, but offers an epideictic (and apodictic) explication of Pompey’s singular suitability for the job. Consider, though: pretty much every member of Rome’s ruling elite considered himself a competent commander (and would have licked his chops at the prospect of finishing off Mithridates). In this light, Cicero’s assertion that there was no plausible alternative to appointing Pompey as supreme commander was not as uncontroversial or even self-evident as it may seem. Indeed, one could just have left the current commander there – for all the current difficulties, even Cicero admits Lucullus has done a remarkable job.
A key aspect of his argument in favour of Pompey is the peculiar mixture of Pompey’s alleged excellences. These included not just traditional hallmarks of distinction such as courage, but also ‘ethical’ qualities grounded in his supposed integrity of character. Cicero will draw this distinction (and elaborate on it) in what follows. Here he sets up this vital part of his argument by slyly delimiting the number of possible candidates by means of two allegedly essential attributes of the appointee, one orthodox, the other surprising (at least from a Roman point of view). In his counterfactual wish introduced by utinam, he obliquely specifies that the commander to be put in charge better be both brave (fortis) and upright (innocens). To claim that Pompey was the only brave living Roman aristocrat would have been silly, so the decisive emphasis in the phrase virorum fortium atque innocentium copiam tantam lies squarely on innocentium. As we shall see, it is not least Cicero’s insistence that bravery be combined with integrity of character that dries up the pool of possible candidates to leave exactly one: Pompey.
A pun that runs through the entire speech reinforces the link between the previous section on the scale of the war and the choice of the general: a war of this particular magnitude (magnitudo) calls for a general who is Magnus.