The U.S. government has lost any shred of credibility and moral authority when it comes to the commission of war crimes, including the supreme war crime that is a war of aggression. We are the nation that cried war — over and over again. From Vietnam to Iraq to Libya, we have demonstrated that not only will we lie to the world just to get our fix of violence and domination, but we'll also leave a path of death, destruction, generational trauma, and even slavery in our wake.
This is exactly why it's so important to oppose wars of choice like Iraq, Afghanistan, and the long list of other American imperialist incursions into sovereign nations across the globe the first place. We are not, can not, and do not deserve to be the world police force.
Who knows? Maybe U.S. intervention would have been on the table if we hadn't spent the last 50 years consistently stomping on the rule of law and the international rules-based order by committing the same (and many, MANY more) war crimes that Russia is currently committing in Ukraine. We'll never know, because we have made ourselves into the posterchild for imperialism, hypocrisy, and impunity for crimes against humanity on the world stage.
In fact, Putin has even been using the same "liberation" rhetoric that U.S. leaders used to justify the invasion and occupation of Iraq; he feels empowered to use Russia's veto power at the U.N. Security Council; and he no doubt has a number of other tricks up his sleeve as the conflict escalates — all direct consequences and models of our own reckless and inhumane foreign policy crimes since the end of WWII.
Maybe — if we were a better nation and if we hadn't spent the last 20+ years waging illegal wars that drained our military might, morale, and public coffers — we might be in a position to intervene on Ukraine's behalf. But we're not, and we did, so we can't.