Given that the potato is from the Americas, did the Russians use other ingredients for making vodka, or did they have a different national drink before the potatoes introduction?
When vodka was first introduced to Russia in the late 14th century, it was made from grape must. The first uniquely Russian variant was made from grains (and was called "Bread Wine"). Prior to that, most people drank beer (pivo) and mead (meod), as well as wine (vino) imported from Greece.
Vodka only became affordable in the late 19th century following a repeal of a government monopoly on its production, so even between the 14th and 19th centuries most people would have been drinking beer and mead.