Go commit a felony and you’ll find out what federal laws local and state cops enforce.
The local and state cops don’t enforce Federal laws. At the most, all they do is arrest someone if there is an arrest warrant, or arrest someone if they’ve violated a state law - and then the Federal authorities may also jump in on it, if there is a Federal law violated.
The states enforce their own laws and the Federal authorities enforce their own laws. They each don’t enforce the “others’ laws”.