Question

nixon not only enunciated his own doctrine, but declared, echoing kennedy, that there could be no winners in a nuclear war, and embarked upon détente with the soviet union and arms - control treaties based upon equality.
source: time
in this sentence, doctrine means:
a statute in draft before it becomes law
a stated government policy, especially regarding foreign affairs
the act of refuting some claim by offering a contrary argument
the process of preparing a nation for war

Explanation:

In the context of the sentence, "doctrine" is related to a policy statement. Nixon's "doctrine" is about foreign - policy stances (such as détente with the Soviet Union). A "stated government policy, especially regarding foreign affairs" fits this context. A statute in draft is more about legislative process (not relevant here). Refuting a claim is about argumentation (not the case). Preparing for war is not indicated by the text (the text is about avoiding nuclear war winners and arms - control).

Answer:

a stated government policy, especially regarding foreign affairs