Lancaster is absolutely commanding in his performance, which you might expect from Lancaster as he has that movie star charisma anyways, but Lancaster kinda does this in a whole different style here. Lancaster is very effective as he makes Hunsecker almost like a snake in which you have to watch and listen to his every movement as you never know who or what he might strike. Lancaster is perhaps at his most imposing here despite he seems to purposefully diminish his usual posture on purpose. Lancaster though brings that incisive quality very much needed to Hunsecker's performance in simply the way he almost leans forward and faces his pretty intimidating them while looking for their weakness for which he will exploit. His opening scene is perfectly executed by Lancaster as Hunsecker humiliates and indicates his superiority over all four of the people around him. Lancaster nails every line as he should giving them the vicious sting they should. Hunsecker's power merely comes from his word and Lancaster establishes this as truth through his performance.
What might be most fiendish in a way about Lancaster's portrayal though is he shows the way Hunsecker can influence. He's not there merely to make fun of the people and make them feel poorly about themselves but also to show how he knows what is right. Lancaster is particularly great as Hunsecker points out to the senator at his table that his affair is quite obvious and that if he's to stay as a respectable politician he better be less obvious about his act. Lancaster does not carry only venom in Hunsecker's words, although there is a deadly dose of that there, he has a teaching tone in his voice as though he is educating in his words. Lancaster importantly gets across that Hunsecker is not merely an acerbic critic of those around him, but that he uses that as his tool to control them even further. Hunsecker ends up controlling the plot because he demands Sidney work something out for him. That something ensuring that Hunsecker's sister Suzy not marry a musician, without Suzy finding out that Hunsecker had anything to do with the breakup.
This brings us to the one side of Hunsecker the perhaps brings out the worst of him as Hunsecker will go any way he can to stop Suzy's marriage even if it means getting the musician fired as well as arrested for a false charge. It does not matter really even who the magician is Hunsecker would hate any man who tries to steal his sister from him. Lancaster does reveal perhaps the only real humanity to Hunsecker in his scenes with his sister. I have read some places that it is incestuous thoughts that propel Hunsecker in these scenes, but I disagree as I don't feel that's how Lancaster plays these scenes. Lancaster I think is far more effective by portraying the quiet moments of thinking of his sister where he creates the only possible sympathy for Hunsecker. It is not a lustful man that Lancaster shows although that does mean he's still not quite creepy. It's fear though that Lancaster suggests as he hears about Suzy's marriage, a palatable fear in a man who knows he would be absolute lone in his world of cynicism if he lost his sister.
Lancaster often is about consistency in the cold brutality that he brings to his performance and the scene where he carefully cuts down the musician, after faking approval, is particularly brilliant. Lancaster is incredibly good here in the later scenes though as he begins to show Hunsecker's reserve to leaves him as he must get more and more involved in Sidney's plan. Lancaster is terrific in portraying a bit of a growing madness in Hunsecker, a quiet yet fervent madness so fitting for Hunsecker, and the intensity grows as he becomes more determined to keep his sister. Lancaster presents Hunsecker as a man who has always been in control, and Suzy perhaps who he has been controlling for the longest time, finally losing his command which is more than he really can comprehend. Lancaster devolves into a mess of sorts though still perfectly as the reserved Hunsecker as everything begins to collapse around him. There are perhaps two Lancasters the wild man, which the best example of is probably Elmer Gantry, and the far more taciturn Lancaster, which best example of may be found here. He gives a great biting portrayal of a villain who does not need to raise a fist to ruin the lives around him.