The tl;dr is not true however. There is binding international law affecting certain treaties, and some kind of treaties and parties do expect ratification from each signatories' internal legislative body.
(e.g. totally random example
https://www.jta.org/archive/french-senate-ratifies-lausanne-...)
Your body is correct though:
Now why the US follows a counter-pattern and why Ukraine did not ask for ratification is another discussion, that I consider to be long term harmful.
From the Ukraine's side/pov: it will be politically not wise for the U.S.A. to back out of the protection treaty. There is good will capital that is lost, just for allowing this 8 year situation to occur.
