I think the reason is important. If you stick to something because you think it is the right thing to do, that is conviction. If you stick to something because you think you must continue as you have already invested effort into, that is sunk cost. The point that I’m trying to make, that perhaps I have not worded well, is that you must act with conviction, because if you do not do what you think is right, you either not do anything, or do what you think is wrong. Sure, you may be wrong at the time, and you should be open to reflection, and not be prey to sunk cost.
But coming up with convenient excuses to avoid doing what you think is inconvenient but right is not how leaders behave.
And in this context (if that is what you mean), it is definitely not evident that supporting Ukraine is a strategy that won’t work.
Hence my apology for the imprecise language. I meant what you said by social democracy, not a social economic system. Anyways, if we’re being pedants, there are no true socialists or capitalists in today’s markets. They’re all mixed-market economies.
When I say socialist (and what is more accurately social democracy), I first think of healthcare, then I think of transit, then of education, and then of utilities. These are things that the US certainly could do better.