In 1946 and 1948 President Harry Truman threatened the Soviets over
Iran and Berlin, respectively, and the Chinese in 1950 and 51.
President Eisenhower also threatened the Chinese over Korea in 1953,
and again in 1956 over Quemoy and Matsu. He offered the French nukes to
use against the Vietnamese at Dienbienphu in 1954.
President Kennedy threatened a nuclear strike at the Soviets over
Berlin, and sent nuclear armed missiles to Turkey on the Russian border
in 1961. Though these were later wisely withdrawn after the nuclear
standoff of the Cuban missile crisis, the US has consistently based its
nukes on its fleets and bases in the Pacific, in Europe and Asia, and
for decades in South Korea.
Presidents Johnson and Nixon menaced North Korea, Vietnam and the
Soviet Union with air and seaborne nukes, and President Gerald Ford
ordered nuclear armed bombers from Guam to loiter for an extended time
off the coast of North Korea. Jimmy Carter issued the Carter Doctrine,
reaffirmed by Ronald Reagan which committed the US to a nuclear response
if its vital interests in the Middle East were every threatened. Ronald
Reagan terrified the world, though he did briefly consider a lasting
arms treaty with the USSR.
Bush 1, Bush 2 and Bill Clinton all menaced North Korea and Iraq, and Obama declared “all options on the table” against Iran.
-- Bruce A. Dixon, "Every US President Makes Unilateral Nuclear Threats. It's an American Tradition" (BLACK AGENDA REPORT).