All options should always be kept on the table
There is no need to disambiguate the role of nuclear weapons and to exclude their use from some particular scenarios. Explicitly listing such scenarios will only encourage enemies to enter those breaches.
"The U.S. has had a long-standing policy, embraced by administrations of both parties, of retaining all options to respond to an attack," Republican Senators John McCain and Jon Kyl said in a joint statement. "The NPR released today confuses this long-standing policy."
"The Obama Administration must clarify that we will take no option off the table to deter attacks against the American people and our allies," the senators said in a joint statement.