Of all the stupid decisions Donald Trump has made a President, the inclusion in his administration’s new national security strategy of a threat to attack non nuclear targets with nuclear weapons surely ranks as the most dangerously stupid of all (“Trump says US could use nuclear weapons against conventional attacks,” 19 December; https://www.theguardian.com/us-news/2017/dec/18/nuclear-weapons-trump-national-security-strategy)
The last time a serving US president threatened the us eof nuclear WMDs against a nonnuclear foe was against China in the Korean war in 1950, when President Harry S. Truman said in a presidential press conference at the White House on 30 November 1950 “We will take whatever steps are necessary to meet the military situation, just as we always have.” When challenged by the press corps with : “ Will that include the atomic bomb ?, Truman retorted “ That includes every weapon that we have…” adding ““There has always been active consideration of its use.” (http://www.presidency.ucsb.edu/ws/?pid=13673
The clear problem with such a strategy is it will encourage non nuclear states that regard to United States as hostile to them - such as Iran and Venezuela- to obtain nuclear weapons to deter US attack; and current small scale nuclear weapons powers, such as North Korea and Pakistan, to build up their atomic arsenals as a future hedge against invasion.
These states will have learned the painful lessons of both Iraq and Libya, whose leaders Saddam Hussein and Muammar Qaddafi, were overthrown after they disarmed themselves of nuclear WMDs.
Columnist Roger Cohen “Trump’s National Security Strategy Is a Farce,” writing in the New York Times, on 19 Dec. (https://www.nytimes.com/2017/12/19/opinion/trump-national-security-strategy-tillerson-haley.html) asserts “President Trump and his team have several contradictory positions. That’s what happens when your priority as president is to use foreign policy to throw red meat to your base while other cabinet members are scrambling to stop Armageddon.
On15 December 2015 Donald Trump said “The biggest problem we have is nuclear—nuclear proliferation and having some maniac, having some madman go out and get a nuclear weapon. That's in my opinion that is the single biggest problem that our country faces right now.”
His new national security posture ensures that will happen.