I think there is a lot of non-nuclear support that Russia could give a terrorist organization. I do worry that eventually Russia will feel that turnabout is fair play, arm our enemies, and push them to act on American soil.
With the border open and the three letter jackboots focused on persecuting traditional Americans what is to stop it?
Russia funding and equipping terrorists would be nothing new. They did a lot of that in the 60s through the 80s, even using Soviet or Eastern Bloc embassies to funnel weapons to the terrorists and circumvent customs inspections.
So if they want to do it again, they don’t even need an “open border”, since they already perfected how to do it with closed borders.