Technically, no.
That said, if the feared North Korean hordes suddenly popped out of their hundreds of tunnels beneath the DMZ and headed south, then you can probably expect that yes, we would contribute military forces to any UN-sponsored force sent to the Korean peninsula to halt this naked aggression.
However, considering more than half the army is already deployed overseas, almost none of the air force‘s CF-18s can work with the USAF because of obsolete equipment, and the navy has decided it‘s taking the next year off, we‘d likely be restricted to harsh words at the UN.
Realistically, of course, the US is not going to let the situation in Korea get out of hand. And unlike in 1950, no one supports the North Koreans, either economically or idealistically -- even the Chinese don‘t want to touch them. The South Korean military is well-trained and well-equipped, and for that matter, so are the Japanese, who I can‘t imagine would just sit back and let the US and RoK fight the DPRK all by themselves -- anti-war constitution notwithstanding.
Frankly, if the political sitation was perfect, I wouldn‘t be surprised if the US launched a pre-emptive strike against North Korea. This is a huge what-if, however, as all the planets and stars would have to be aligned just so, and in the end, is probably as unrealistic as a North Korea invasion of the south.
