If you have ever discussed this with a Calvinist then you will probably have encountered the circular thinking which typifies the Reformed attitude to God’s sovereignty. Essentially, they will pre-define sovereignty as God being able to do anything he can without fear of contradiction or being shown to be in the wrong. Of course once you have defined it like this, then the Reformed position does look sensible. But this is simply because you have defined sovereignty as being such and such and then arguing that anything which doesn’t conform to this must be bringing God’s sovereignty into question.
When you look at the Bible narrative you find it is replete with examples of people who do things which God doesn’t want them to do. So the logical thing is to say either God is purposing them to do these wrong things or that they are in fact of their own free will going against God’s will. Does this behaviour then constitute a challenge to God’s sovereignty?