The real question to be had here is what was a popularis? For this I'll borrow Tatum's definition, which is pretty succinct and cuts to the chase nicely. Tatum correctly notes that the popularis politician is frequently misunderstood by students of the Roman world when they first encounter him, because of "the modern tendency to see the choice of the via popularis either as mere politicism or as an expression of social altruism, as if this dichotomy were inevitable or even natural." Instead, as Tatum points out, the popularis politician was quite simply any individual who turned first and foremost to the citizen assemblies, particularly the tribal assembly, for political support, spurning the support of the senate at large. With this often came "populist" legislation, though more usually the popularis proposed a mixed bag--Gaius Gracchus, a staunch aristocrat, offered agrarian bills alongside a bill that limited the powers of the tribunes of the plebs. It must be noted from this that, in Tatum's words, "the ideological background that supported popular rights was by no means alien or hostile to the aristocratic perspective." In fact, I would even go one further and suggest that the "conservative" elements of the senatorial class in the earlier part of the first century were the main defenders of the rights of the urban plebs, as few tribunes or other populares bothered much with the urban poor at all, focusing their attention almost solely on the Italians and rural citizens. The populares were not a political party. Though we sometimes use the word as a shorthand (e.g. in Lily Ross Taylor's book Party Politics in the Age of Caesar, in which she doesn't talk about parties at all) the Roman world knew nothing approaching the political party. Politics was a decidedly individualistic, highly competitive enterprise that pitted the personalities and public existences of notable individuals against each other. The idea of a political party would have been antithetical to the way a Roman thought of politics. The popularis simply turned to the populus Romanus first and foremost. He might have various reasons for doing so. Often, Cicero asserts, the cause of a popularis politician's actions were out of dolor, the wounding of his dignitas. Sulpicius Rufus, Cicero believed, turned to Marius and popularis tactics after his dignitas was wounded by Pompeius Rufus, whom he had helped and whom he counted as a friend. Domitius Ahenobarbus proposed the decidedly popularis measure of transferring priestly elections to the citizen assemblies, resulting in his election as pontifex maximus the next year, after the college of augurs refused to co-opt him into their number. Sometimes the popularis acted out of genuinely altruistic motives--I'm inclined to believe that the Gracchi legitimately believed there was some problem in the population of the rural districts. To some probably the promise of popularity itself was enough of a reason to turn towards the via popularis--Plutarch reports that Pompey dreamed before Pharsalus that he would enter his theater amid great applause. Pinning down the precise motive for a popularis politician's turn towards such tactics is in most cases futile, but these are at least the kinds of things pointed to by the Roman authors themselves.

What becomes immediately obvious from all of this is that the popularis politician was not bound by his popularis aura, to borrow Cicero's phrase. He might drift to popularis tactics for various reasons, but there was no reason why he needed to stay there. Even the staunchest supporters of senatorial preeminence might don their popularis hats every now and then. When Cicero delivered the de lege agraria Cicero presents himself as a popularis, appealing to the people against the tyranny of Rullus' proposed agrarian bill. The tactic was stunningly successful, despite the fact that the bill theoretically should have been supported by the people (in fact I do not think it should have been at all--the urban plebs rarely supported agrarian bills, which tended to benefit the rural plebs, not them). When tribune in 63 Marcus Cato proposed an expanded lex de frumentaria even as he launched into a tirade in the senate advocating for the execution of the Catilinarians without trial.

That Pompey was a popularis for a great part of his career is abundantly obvious. Pompey inherited the patronage of large swathes of Italy from his father, and as Sulla's protege could call up support from throughout Picenum and all the way up to Cisalpine Gaul. These clients served him throughout his life, providing him with much-needed manpower when his struggle against Publius Clodius turned against him in the 50s, packing the citizen assemblies in order to force the recall of Cicero, and causing Pompey to confidently boast that he need only stamp his foot in Italy and he would be greeted by loyal armies. To a certain extent, then, Pompey began his career as a popularis, as he relied extensively on the support of these clients during his early rise to power--at the same time, of course, Pompey was firmly in Sulla's camp. Pompey's highly successful military career--still without senatorial magistracy, an aberration to the senatorial class--netted him immense popularity throughout the 70s, culminating in his consulship alongside Crassus in 70. This consulship involved the repeal of a number of particularly unpopular Sullan measures, notably the restoration of the powers of the tribunes and the re-establishment of the equites in the law courts, both decidedly popularis bills. Pompey's military career often followed his career as a popularis, and throughout the 60s Pompey's command first against the pirates (which lowered grain prices in the city and garnered Pompey near-total support among the urban plebs) and against Mithridates garnered him great attention and popularity. It also gained him the suspicion of the senatorial class, which was never pleased to see one of their number--especially not one so unusual as Pompey--rise so high without withdrawing back into their ranks. Much of Pompey's popularity coincided, then, with incredible hostility from the senatorial class, which continued into Caesar's consulship. Pompey and the other triumvirs quickly lost the support of the urban plebs, however, who famously demanded endless encores of the line nostra miseria tu es magnus at the theater, and snubbed Caesar but applauded Curio's entrance to the theater. But Pompey's enormous influence throughout Italy outside the city is hard to understate. This rural support was Pompey's primary political weapon, apart from his own personal influence, throughout the 50s. Pompey's repeated victories at the citizen assemblies, which could be strongarmed by rural voters easily, were largely a result of this rural support, even as Clodius tried to organize the urban plebs more systematically for the vote, with stunning successes early on. Even as late as Pharsalus, if we are to believe Plutarch, Pompey still had popularis ambitions--recall that he was said to have dreamed of his own popularity.

Can we speak of Pompey actually turning away from his via popularis? Possibly. Pompey briefly managed to snatch away some of the loyalty of the urban plebs when he took over the cura annonae, but by 52 he had decisively lost that fight. Clodius' murder and the pseudo-dictatorial response that the senate empowered Pompey with cannot have been viewed favorably by the urban plebs, many of whom were silenced or massacred by his soldiers. As late as 55, however, he was still tied to Caesar and Crassus--the renewal of the triumvirate, when the senatorial class refused to support Pompey any more than was absolutely necessary, in 56 drove a wedge between Pompey and Cicero, as was its intention. Notably, of course, Caesar's bids for consular reelection revolved around popular sovereignty. Pompey and Cato rejected the right of the tribal assembly to allow Caesar to run in absentia by plebiscite, and in his personal struggle against Caesar eventually went so far as to violate the sacrosanctity of the tribunes. But was this really a turn towards the optimates (themselves not a political party, and ideologically even hazier than the populares)? Certainly Cato and Scipio sided with Pompey. But they viewed him with distrust, as he did them. To the Catos of the senate, faced with the distasteful threat of seeing Caesar hold the consulship once more, Pompey was the lesser of two evils, as Gelzer put it. To Pompey the senatorial class, which had despised him for so long, was finally behind him, and it was no longer worth suppressing his personal conflict with Caesar. Neither man flinched, although Caesar repeatedly offered concessions--it should be noted that the senate voted overwhelmingly in support of Caesar's suggestion that both he and Pompey lay down their arms, which Scipio basically ignored. Rather than some ideological shift (to Pompey, like Caesar, the primary ideology was individual preeminence) I think it would be more correct to understand Pompey's turn towards Cato, who finally expressed support for him after decades of hatred, as a useful alliance between two disparate elements.