Jim "Boss" Gettys is your typical corrupt politician. Everyone knows he's corrupt, but no one has the money or power to take him on in New York's election for governor… until Charles Foster Kane hits the scene.
Kane runs out to a huge lead in the polls and threatens to throw Gettys in jail for all the backroom deals he's made. So it's quite true when Gettys says,
GETTYS: Now I'm going to lay all my cards on the table. I'm fighting for my life. Not just my political life. My life.
Kane is so relentless in his attacks that Gettys becomes desperate. And when he finds out about Kane's affair with Susan Alexander, he gets the "Get Out Of Jail Free" card he's been waiting for.
Now that he has the upper hand, Gettys tries to blackmail Kane into dropping out of the election. In this sense, he's actually being fairly reasonable, as he says,
GETTYS: That's the chance I'm willing to give you, Mr. Kane. More of a chance than you'd give me.
But the fact remains that Gettys is a crooked jerk who will do whatever it takes to stay in power. That said, he also knows another crooked jerk when he sees one, as he says to Kane,
GETTYS: Only you're going to need more than one lesson. And you're going to get more than one lesson.
Even though he's corrupt, Gettys is actually quite accurate in what he says here. He recognizes that Kane is too proud to learn from his mistakes, and that'll bring Kane nothing but pain and frustration for the rest of his life.