Do States have to enforce Federal Laws?

In my government book it says that congress may not compel states to enact in compliance with federal standards or compel them to enforce federal laws. I am confused about this because I thought that laws made by the federal government took precedent over laws created by states. I thought that federal law was the... show more In my government book it says that congress may not compel states to enact in compliance with federal standards or compel them to enforce federal laws. I am confused about this because I thought that laws made by the federal government took precedent over laws created by states. I thought that federal law was the "Law of the land", can anyone explain this to me?
Update: Thank you. That was very helpful, it makes a lot more sense now. :-)
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