Samuel has been criticizing the policies of the state government, which has led law enforcement officials to conduct a raid on his home. he could be protected, though, by which constitutional amendment?

The Fourth amendment specifies that there should be a search warrant to allow a search.  The amendment protects the right to privacy of the people.  
A warrantless search is a violation of this law and can be a subject to bien action, a case filed against the government if during the search some property was destroyed.