Cataline (who carried Marius' standard in battle)

Catiline's soldiers also were in large part apparently Sullan veterans (Sallust, B.C., 16), Sallust's (difficult to interpret) description of the reaction of the urban plebs has them eager for Sullan proscriptions (Ibid., 37), and Lentulus apparently compared himself to Cinna and Sulla (Ibid., 47).

Caesar (who paraded Marius' image at his aunt's funeral and prosecuted the "murderer" of Saturninus)

Labienus prosecuted Saturninus, who was executed by Marius, as tribune. Though he had to revive an archaic law to prosecute Rabirius, as there is no known case of an individual ever being prosecuted for violation of tribunician sacrosanctity, the tribunician character of the prosecution is clear, and of a nature very similar to the tribune Nepos' refusal to allow Cicero to deliver a farewell oration at the end of his consulship, apparently because of Cicero's execution of Roman citizens and a sitting magistrate (Lentulus) without trial. Caesar's aunt Julia had been Marius' wife, and while Caesar's public honors to Marius in his youth were somewhat unusual such things were neither unprecedented nor, from the young Caesar, particularly unsurprising. Caesar had spent much of his life fleeing Sulla, and Gelzer makes a good case that Caesar was effectively a Marian partisan in the earliest part of his career. In any case these sorts of resumptions of predecessors' careers were hardly unprecedented. Plutarch describes C. Gracchus' tribunate as a continuation of his brother's (though I find more differences than similarities), and the tribune Sex. Titius the year after Saturninus' death appears to have continued championing agrarian bills like his predecessor and was condemned and exiled for possessing an image of Marius (Julius Obsequens, 46; Cic., Rab. Per., 24-25).

Cicero refers positively to him in his 4th Catalinarian oration (?). Was this meant to play at popular support?

The Fourth Catilinarian was delivered in senatu, not in a contio like the Third Catilinarian. It therefore could not have been a popularis speech, and shows no signs of being so. Cicero was a native of Marius' hometown Arpinum, and as such he mentions him with praise frequently, especially at the beginning of the de legibus and in the de divinatione, in which Quintus refers to Cicero's now lost epic poem the Marius.

The point of the above is that the cases here are hardly straightforward, nor is the use of these as evidence for the urban plebs. The modern sorting of Marius and Sulla into "populist" and "aristocratic" camps is primarily a modern one, influenced by Mommsen's interpretation of Republican history as analogous to the politics of his own contemporary Germany. The sorting is implicit in your comparison between Democrats and Republicans--the comparison is not there in the sources. Roman writers, themselves the learned aristocracy, described Marius and Sulla as similar as often as they described them as different. Lucan begins Book 2 with a remembering of Marius and Sulla, praising them for their outstanding qualities but condemning them for the bloodshed that they caused. Caesar says (B.C., 1.4) that Lentulus boasted to his friends on the eve of the civil war that he (Lentulus) would be a second Sulla, specifically equating Sulla to the summa imperii, highest military command. In this same vein should be taken Cicero's comment from the Fourth Catilinarian. Cicero praises Marius for his military command and his action rescuing Italy from the Teutones and the Cimbri. This is typical, across all Roman writers: Sulla and Marius among the literate were remembered for their military campaigns, which rightfully were seen as triumphs of ability, and for the civil bloodshed that Marius' executions and Sulla's proscriptions caused after the fighting. The man could be praised and condemned in the same breath, without much trouble. Such characterizations are not uncommon. The Roman writer and orator did not understand human beings, particularly not those thought to have outstanding and notable natures, as being one-sided. To Roman moralism that combination of flaws and strengths was one of the things that made "great men" so great.

But typically in literature and oratory where attention is drawn to Marius and Sulla it is drawn to their military abilities and to the loss of Roman life that resulted from their seizures of power. Now, occasionally the two individuals are used as examples of anti-aristocratic or anti-popular positions, particularly the former. Sallust in the B.J. uses Marius as the voice of discontent, specifically with the way the learned aristocracy fights war without experience. Caesar at the beginning of the B.C. (1.7) condemns Sulla for constraining the powers of the tribunes, and associates Pompey with Sulla for further debasing the tribunate by attempting to remove their veto, which Caesar notes Sulla had left them. Nonetheless, the differences in their depictions, which are less frequent than their general association with civil bloodshed and military achievement, should not lead us to conclude that the Romans saw them as occupying opposite ends of an ideological divide. It would be too much to say that there were no ideological divides in Republican politics--that model, which John North called the "frozen waste," has been abandoned for decades--but while the modern pop historian might want to characterize Marius and Sulla as "populist" and "conservative" (and frequently does), the characterization does not seem based on what either of them did nor on how the Romans understood them. Our aristocratic writers routinely condemn Marius for various civil actions while praising his military abilities. They do exactly the same thing for Sulla, who it must be noted had a much greater civil impact--Marius basically had no domestic actions, except if we trace Saturninus' agrarian bill back to him, which seems suspect. You can find on wikipedia or in pop historians assertions that Sulla aided the senate or the magistrates or whatever with this or that act, but those are merely the musings of pop historians, usually working from scholarship decades out of date (if they're using any at all). We find no such assertions from our sources. No aristocrat says that Sulla was a great guy for reducing the power of the tribunes. No aristocrat in our sources has anything but scorn for Sulla's use of the dictatorship and his implementation of the proscriptions, for which he was typically remembered more than for anything else. Likewise, plenty of aristocrats in our sources think of Marius with praise and great pride, if it weren't for that whole killing Roman citizens thing.

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