Russia has been incrementally seizing Georgian land, to the point it occupies 20% of its territory. If Georgia joined NATO, that might short-circuit further Russian expansion, which is presumably why Medvedev is getting all riled up about that possibility. Russia has always considered any move to prevent its territorial expansion to be provocative, and the possible Georgian accession to NATO is no exception.
https://www.businessinsider.com/russia-quietly-seizing-territory-in-georgia-10-years-after-the-war-2018-8
[Vice President Mike Pence made similar remarks on a visit to Georgia last year.
“Today, Russia continues to occupy one-fifth of Georgian territory,” Pence said . “So, to be clear — the United States of America strongly condemns Russia’s occupation on Georgia’s soil.” ]
Do you believe Georgia is in the essential interests of the US?
Is their territorial integrity worth a single US life?
How about a US city?
That 1/5 is also known as Abkhazia, which from the perspective of Russia is not occupied, but has their own government. The Georgians refuse to recognize the secession, but the reality is that they are independent.