How Much of a Threat Does Claudius Consider Hamlet?

I think Claudius considers Hamlet a formidable threat, because it seems that he is a little too overly concerned about Hamlet and why he has gone crazy. It is perfectly natural for a parent to be concerned and try to figure out what is causing this change, however I think Claudius goes a little overboard. It seems that no matter what is going on around him, he wants to know about Hamlet. A great example of this is in Act 2, Scene 2, when Voltimand brings news that Fortinbras does not want to fight him anymore, but rather wants safe passage through so they can go fight the Polish. Instead of tending to this important business, Claudius tells Voltimand, "at our more considered time we'll read, answer, and think upon this business"(81-82). If Claudius does not consider Hamlet much of a threat, I do not see why he would have blown off national matters in order to tend to personal matters. Hamlet is a big enough threat to Claudius to cause him to abandon his responsibilities and duties as King. I do not believe that Claudius knows Hamlet saw his father's ghost, however it seems he believes Hamlet knows a little more than he would like.