If the Russians are rational (your words) then stopping them now, while it is relatively easy, will not lead to “existential war”.
However, the Russians consider everything they do, geopolitically, to be “defensive”, regardless of whether anyone else sees it that way or not. Gingrich is correct in pointing this out. Putin’s own words about centuries of “containment” are the key.
Now, the difference between C.A.R. and Ukraine or Estonia is that we have (well, HAD, since we evidently are “without honor”) a very serious security agreement with Ukraine, not to mention that the majority of the people there understand and quite sincerely want to be a Western style democracy. Estonia is even more serious a security commitment (NATO ally) and is a rather well functioning “Western” democracy and economy in fact. C.A.R. is the opposite, with even its
Prime Minister Nicolas Tiangaye saying it is a “non-state”.
The ramifications of the US abandoning these commitments is devastating: It not only encourages aggressions now and in the future, but even worse, unless a Russia / China axis becomes totally dominant, quickly, it almost guarantees at least a mid-scale nuclear war down the line.
A Presidential signature on a document isn' t worth squat. Everyone in the world knows that.
Without Senate Ratification of a Treaty the USA did not commit to anything concerning Ukraine.
Asw for the majority of the Ukrainian people, they voted for a pro-Russian president in a free and open election.
As for NATO? We need to STOP it's expansion, and now. NOBODY in the US wants to go to war to defend Ukraine or Georgia.
Yeah, we have to honor our commitment to the Baltics, Romania and Bulgaria (really, Bulgaria?), but we needn't make such folly worse.