This is a pretty easy call for the White House because the American public will be calling for North Korea to be turned into a glowing parking lot of they fired nuclear weapons at South Korea and the U.S. troops stationed there:
South Korea and the United States agreed to take “swift, overwhelming and decisive” action using all of their military capabilities, including U.S. nuclear weapons, in the event of North Korea’s nuclear attack, President Yoon Suk Yeol said Wednesday.
Yoon made the remark during a joint press conference with U.S. President Joe Biden following their summit talks at the White House, outlining a joint statement, dubbed the “Washington Declaration”, that they adopted to strengthen “extended deterrence” against the North’s nuclear and missile threats.
Yonhap
You can read more at the link.