What constitutional issue arose when Truman ordered troops to Korea?

Truman faced the issue of being able to interfere in foreign matters that the restriction were put in place for.

Explanation:

After the second world war the US government had tried to make it harder for the US to go to war by making it harder to justify the reasons of engaging in foreign wars for the country.

When Truman entered the war in Korea he wanted something that would explain away the assailant nature of the quest.

He found it when the UN itself agreed to intervene in the matter against Russia in the only case such that happened in the world history.