The options are stark:
A pre-emptive attack on its missile launching facilities. Doable but reckless. It is the option most likely to trigger an actual war. The North Koreans enjoy both conventional superiority and proximity: a vast army poised at the Demilitarized Zone only 30 miles from Seoul. Americans are not going to fight another land war in Asia.
Shoot down the test ICBM, as advocated by The Wall Street Journal. Assuming we can. Democrats have done their best to abort or slow down anti-missile defenses since Ronald Reagan proposed them in the early 1980s. Even so, we should be able to intercept a single, relatively primitive ICBM of the sort North Korea might be capable of. Though such a shoot-down would occur nowhere near North Korean soil, it could still very well provoke a military response. Which is why the new administration should issue a clear warning that if such a test missile is launched, we will bring it down. Barack Obama is gone. Such a red line could be a powerful deterrent.
Return tactical U.S. nuclear weapons to South Korea.