Russian forces have always had a reputation for being tenacious fighters, and previous conflicts have historically shown their willingness to accept/tolerate staggering casualties while still maintaining the will to fight. But they suffer from the same challenges any military faces, including exorbitant maintenance and logistics costs for their most important assets. We deal with it, every nation deals with it. This is a different era, though, and the technology gap between Russia and the US is far wider now than it was even 20 years ago. In a large scale conflict where they attempt to decimate our military and we vice-versa, there'd be little they could do, as we still can achieve air superiority over them. Their Navy would be ended in a week and a half. Collectively on the ground we'd still own the night against them.
Where it gets murky, though, is at what point tactical (nuclear) warheads get implemented- which they eventually would. At that point, everybody loses.
That's why I argue we don't wait for Estonia or Latvia or Lithuania to fall before we make a scene. We make it an issue now, so we're not having this discussion again after the fall of other former Soviet republics.