Apex domains cannot have CNAME records.
Question and response
Question
dig spf.usa.net. NS
Answer
spf.usa.net. 5 NS dnsext01.usa.net.
spf.usa.net. 5 NS dnsext02.usa.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0