They already have a foothold in Transnistria. Like Georgia, they've been slowly working on invading by inserting Russians into occupied areas then claiming "Look, we're Russian. The locals are oppressing us. We need to bring in more military to keep Russians safe."

I'm not that educated on the current situation and am oversimplifying what I think I know, but Russia pretty much controls Transnistria and there is a huge weapons depot there.