Character Analysis
Cardinal Campeius is sent by the Pope to England to see what's up with the whole divorce thing. He's supposed to figure out whether Henry's divorce should be legal from the Church's point of view; what he actually does, however, is ruffle a bunch of feathers. For example, he teams up with Wolsey in the divorce trial against Katherine, which makes us think the guy is up to no good. He also gets all hypocritical when he councils Katherine: "Put your main cause into the King's protection" (3.1.105).
Katherine, of course, isn't having any of it. Henry himself doesn't trust the guy at all; he whispers to us: "I may perceive / These Cardinals trifle with me. I abhor / This dilatory sloth and tricks of Rome" (2.4.260-262). Henry's smart enough to realize that if anyone is equal to him in power, it's the Pope in Rome. He knows better than to trust any representatives of the Pope, and maybe that's why it's easier for him to see through Campeius than it is for him to see through Wolsey.
We guess the real question when it comes to Cardinal Campeius is whether or not he's in it to win it with Wolsey. Sure, the two cardinals are pretty cozy, but we don't know if he's in on the letters Wolsey has been secretly sending the Pope. Campeius packs his bags mighty fast once Wolsey's pen pal has been discovered, but that doesn't necessarily mean he knew what was going on.
Shakespeare leaves it up to us decide: is the guy a pawn or a player?