That judge went after one of the largest corruption scandals of our age. There's no evidence he did so in order to acquire a political position: at the heyday of the prosecutions against the workers party, the current president (who made the judge one of his ministers) wasn't even widely known by the population.
On the other hand, Greenwald, who works for The Intercept and is funded by Pierre Omidyar (one of Ebay's founders), has a very strong leftist agenda (he's a regular in communist conventions and whatnot, for that matter), and has been working in all ways possible to discredit the current government while praising the previous government which was impeached -- the one whose party members have been convicted by various crimes, mostly corruption related. It's hard to argue that Greenwald was exposing some sort of manipulation by the judicial system. He was trying to manipulate the media by creating a narrative using information that he acquired illegally, and that he couldn't use to demonstrate wrongdoing in the end of the story.
It's not hard to argue at all - it's exactly what he did.
The leaked texts make it clear that the prosecutor's office and the judge (Moro) had clear political motivations for taking down the front-running candidate in the last election and that they abused their powers to do so.
At the time the bulk of the investigations were happening, Lula wasn't even running for president, and the elections were quite far away (4-6 years), so you can't argue he was in the front-run of the election.
All this political activity is revealed by Greenwald's reporting on the leaked messages.
Also, do you really believe that could have changed the outcome of the elections?
It's interesting to note that Greenwald keeps playing the key that Moro did "politically motivated" actions (disregarding the fact the legal actions against the worker's party went through about a dozen judges beyond Moro), while Greenwald himself is doing "journalism" that is "politically motivated".
A few points:
1. The judge can talk to anyone (freedom of expression here). He would incur in a crime if his ruling favored one side disregarding the evidences
2. Greenwald associated himself with a group that hacked Moro's phone so that they could steal potentially incriminating information. He's being prosecuted because of that act, not because of his political agenda, or because "the government" is trying to cease his freedom of expression
3. The uncovered conversations between Moro and the prosecutors didn't uncover wrongdoing, as far as the law is concerned. Moro was open about his talks with the prosecutors and defense about 4 years ago, so that alleged "coordination" wasn't exactly "hidden"
4. Moro didn't "lead" any groups. All the cases that put many workers' party leaders in jail were judged by many other judges, in different stances of the judiciary, including the supreme court which is highly favorable of the workers party to this day
In essence this whole story is a smoke screen to try to incriminate a Judge and "forget" about the crimes committed by the workers party leaders by stating that "because Moro talked to prosecutors, the rulings were biased", and by stating that "a heroic journalist is having his freedoms of expression persecuted" while that journalist committed a crime exactly on the grounds of stopping other people to communicate by invading and stealing data from their devices.
Anyways, if it is, Greenwald has been one of the most outspoken critics of many aspects of the Russiagate accusations against Trump(1); and in consideration of your aforementioned "liberal agenda" of his, it hardly makes any sense at all to label him on this hand a Trump defender--as he has been accused of--and on the other a 'liberal commie.'
1-https://theintercept.com/2019/01/20/beyond-buzzfeed-the-10-w...
Greenwald has been criticizing Russiagate, but he's certainly not supporting Trump. He's very far from being a Trump defender if you've been following his work.