The US has legal reasons now. Ukraine is a sovereign country and would be more than happy to accept US military bases. The US hasn't sent soldiers because they don't want to go to war with Russia
If US owned resources in Ukraine, they have very good reason to deploy troops over there. Russia won't escalate the situation by attacking american resources and troop. This should slow down the war to a good extent combined with the cease fire agreements.
After all, why would the US get involved when they don't need the minerals they'd have to lose?
Sad to see how Trump is dismantling USA from it's role as a global superpower.
2. US France UK has made it very clear that they can occupy and establish military bases in non nuclear countries without repercussions, especially in Middle East and Africa.
3. Memorandum was signed by multiple nuclear countries and none of thier troops are deployed in Ukraine. Besides US was the largest supplier of weapons in Ukraine.
US is hardly affected by Ukr situation. For them to get involved, there should be something at stake. If they owned something in Ukr, they would have reason to defend it with US troops. Russia won't escalate by attacking US troops or resources.
And if getting involved will escalate to ww3, what difference does those resource deals make? Either american involvement (via NATO or this mineral deal logic) forces Russia to back down or it doesn't.