“We don’t have any commitments to Ukraine...”
So sayeth you, but in reality we guaranteed their national sovereignty, a sovereignty that Russia is currently threatening.
“nor do principles require us to make Americans suffer for their benefit”
Principles require that if you have them, you stand on them whether it causes you to suffer or not.
yet there are none at stake here.
If you're referring to the Budapest Memorandum in 1994, it obliged no such thing.
What it did oblige (as far as it could, since it carried no enforcement mechanisms as a treaty would) was for the parties to resort to the UN Security Council.
To this point, as far as I'm aware, the UN Security Council has not authorized military aid or action on behalf of member states to defend Ukraine; so unless you're referring to an entirely different treaty wherein the United States "guaranteed [Ukraine's] national sovereignty", relying on this Memorandum to buttress this claim is without merit.