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Ukraine didn’t cease to exist when the administration was removed. Why would you think that would be the case? They still go by the same name and hold to all their relative treaties other than those involved in their invasion.
We have all sorts of agreements with Ukraine including ones that provide military responses which seems to be a fairly significant sign they are an ally. They are not any more now that the USA is aligned with Russia once again.
Why would you think the Ukrainian government isn’t an ally of the USA? Why would you think the treaties and agreements made by previous administrations aren’t still in place?
They might not have known what mutual aid is and you explained it very well with the first two sentences. The last sentence doesn’t serve any useful purpose if they didn’t know.