1. Hamlet's madness: Claudius claims that Hamlet is "mad as the sea and wind," and that any attempt to arrest him would only further inflame his insanity. This suggests that Hamlet's unpredictable behavior makes him too dangerous to deal with directly.
2. The people's love for Hamlet: Claudius states that the people of Denmark have great affection for Hamlet, and that any attempt to arrest him would be met with strong opposition. He implies that Hamlet is a popular figure, and that the public would likely rise up in his defense.
Claudius uses these two reasons as a way to deflect blame from himself and to portray Hamlet as a dangerous and unpredictable individual. It is important to note that these are only the reasons Claudius offers, and the audience is left to decide whether they believe him.